Structural diversity and photocurrent responses of multi-component chalcogenidometalates

Abstract

Multi-component chalcogenidometalates have garnered significant attention due to their promising applications in solar energy conversion devices, including photodetectors, solar cells, and photocatalysts. Photocurrent response is not only a fundamental property of photodetectors but also serves as a key indicator of the solar energy conversion efficiency in potential semiconductor devices. Despite the growing interest, a clear and universal guideline for designing chalcogenide materials with excellent photocurrent response remains elusive, primarily due to the substantial variations in their chemical compositions and crystal structures. In this review, we present a comprehensive compilation of reported multi-component chalcogenidometalates, including main group chalcogenides with binary and ternary anionic frameworks, and discuss their photocurrent response performance. Additionally, we also highlight other special chalcogenide systems, focusing on their photocurrent response characteristics. For the first time, we systematically summarize the intricate relationships between chemical composition, crystal structure, electronic band structure, and photocurrent response in these materials. Finally, we believe that this review provides a valuable structural perspective on the photocurrent response of multi-component chalcogenidometalates, offering useful insights for the design and application of advanced solar energy conversion materials.

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1. Introduction

Chalcogenidometalates have gained widespread attention for their promising applications in solar energy conversion technologies due to their semiconductor properties. These materials can generally be classified into two categories based on the composition of their basic building units (BBUs). The first category includes binary chalcogenides composed of a single transition metal, such as MoQ₂, WQ₂, CdQ, and HgQ (where Q = S, Se, or Te). The second category encompasses compounds with main group metal atoms like Ga, In, Ge, Sn, Sb, and As, most of which coordinate with transition-metal-based (TM-based) BBUs to form binary or ternary multi-component anionic structures. The incorporation of additional structural and functional units can significantly alter the electronic structures and physical properties of these materials, distinguishing them from the original binary anion compounds. By selecting appropriate structural or functional units, it is possible to design multifunctional materials tailored to specific applications. In general, multi-component chalcogenidometalates are composed of organic or inorganic charge-balancing cations and metal-containing anion skeletons, which exhibit a wide range of network topologies. These include zero-dimensional (0D) clusters, one-dimensional (1D) chains, two-dimensional (2D) layers, and three-dimensional (3D) frameworks. The diversity in their structures and compositions has led to extensive exploration of their potential in various fields, such as nonlinear optics,¹ thermoelectrics,² superconductors,³ magnetism,⁴ photocatalysis,⁵ ion exchange,⁶ and photoelectric devices.⁷

A wide range of materials have been investigated for solar energy conversion, including silicon/carbon-based compounds, oxides, and simple chalcogenides, with optical band gaps ranging from 1.23 to 3.1 eV. Silicon-based solar cells, as first-generation materials, typically demonstrate relatively high conversion efficiency, with a photocurrent density around 35 μA cm⁻².⁸ However, since silicon naturally occurs as SiO₂ in sand and gravel, its purification requires significant energy input, and the yield is low. Additionally, converting silicon ingots into wafers is a challenging process. As a result, finding alternative solar cell materials could significantly reduce costs. Most metal oxides, such as TiO₂ (3.0 eV),⁹ ZnO (3.2 eV),¹⁰ and SrTiO₃ (3.25 eV),¹¹ have wide band gaps, limiting their absorption to ultraviolet light only. For example, TiO₂ nanowire arrays produce a photocurrent density of 3 μA cm⁻², which can increase to 0.76 mA cm⁻² through carbon/nitrogen co-implantation.¹² Perovskite solar cells typically exhibit a photocurrent density of around 20 μA cm⁻².¹³ In contrast, chalcogenides, with their narrower band gaps, are more effective at absorbing visible light and have been extensively explored for solar energy conversion. Notable chalcogenide materials include CdTe and CuInGaSe (CIGS), which are widely used in commercial solar cells. CdTe thin-film solar cells typically show a photocurrent density between 20 and 25 mA cm⁻²,¹⁴ while CIGS thin-film solar cells generally have a photocurrent density around 30 mA cm⁻², with high-performance variants exceeding 35 mA cm⁻² in laboratory settings.¹⁵ Among various metal chalcogenides, multi-component chalcogenidometalates offer diverse network topologies and tunable optical band structures due to their adjustable chemical composition, making them promising candidates for high-performance solar energy conversion materials.

Despite the large number of multi-component chalcogenidometalates that have been synthesized and studied, a comprehensive summary on the design and synthesis of high-performance chalcogenides for solar energy conversion applications remains lacking. According to the Shockley–Queisser criteria,¹⁶ the optimal band gap for a light-absorbing material is around 1.3 eV. The Spectroscopic Limited Maximum Efficiency (SLME) theory¹⁷ provides a calculable metric for selecting suitable photovoltaic absorbers, specifically for the I_pIII_qVI_r chalcopyrite materials, through a more detailed analysis of their band structures. However, these criteria have proven to be insufficient, as numerous compounds with diverse chemical compositions, structural characteristics, and electronic band structures have been developed in recent decades, and not all of them adhere to these criteria in terms of their solar energy conversion efficiency. Photocurrent response is a fundamental property of photoelectric devices and serves as a critical indicator of the solar energy conversion efficiency of potential semiconductor materials. This work, therefore, focuses on multi-component chalcogenidometalates and their photocurrent response properties, aiming to provide insights for the development of advanced materials for solar energy conversion technologies.

In this review, we present a comprehensive collection and discussion of reported multi-component chalcogenidometalates, which are classified into four distinct structural types: 0D clusters, 1D chains, 2D layers, and 3D frameworks. These materials belong to five crystal systems and a total of 26 space groups. A statistical analysis of the multi-component chalcogenidometalates with reported photocurrent response experiments is provided, as shown in Fig. 1. Notably, the majority of these materials fall within the monoclinic crystal system, accounting for approximately 50%, and more than 55% exhibit photocurrent densities ranging from 2 to 50 μA cm⁻². The details of the synthetic conditions, crystal systems, space groups, structural dimensions, optical band gaps, and photocurrent densities are summarized in Table 1 in the following sections.^18–54 Additionally, we systematically investigate and summarize the relationships between chemical composition, structural characteristic, electronic band structure, and photocurrent performance. This analysis offers new insights into the design and optimization of chalcogenidometalates for enhanced photocurrent responses. It is our hope that this review will serve as a valuable resource for advancing the understanding and study of photocurrent behaviors in multi-component chalcogenidometalates, facilitating their development for future applications in solar energy conversion and related technologies.

Fig. 1 Distributions of the reported chalcogenidometalates in (a) crystal systems, (b) photocurrent density intervals (ranging from 0–1 μA cm⁻², 2–50 μA cm⁻², and 51–200 μA cm⁻²), and (c) space groups.

Table 1 A summary of the reported multi-component chalcogenidometalates exhibiting photocurrent responses

No.	Formula	Crystal system	Space group	Dimension	Synthetic method	Band gap (eV)	Photocurrent density (μA cm^−2)	Ref.
1	[Mn2(en)4Ge2S6]n	Monoclinic	P21/c (no. 14)	1D	Solvothermal synthesis	3.27	1.2	18
2	[Mn2(dap)4Ge2S6]n	Monoclinic	P21/c (no. 14)	1D	Solvothermal synthesis	2.87	1.9	18
3	[V(en)2(ea)]2[Ge2Se6]	Monoclinic	P21/n (no. 14)	0D	Solvothermal synthesis	2.44	30.8	18
4	[V(teta)(ea)]2[Ge2Se6]	Monoclinic	P21/n (no. 14)	0D	Solvothermal synthesis	2.47	16.1	18
5	[V2(en)6(μ-O)][Ge2Se6]	Triclinic	P1̄ (no. 2)	0D	Solvothermal synthesis	1.66	22.8	18
6	[V^II(dien)2]2[Sn2Se6]	Monoclinic	P21/c (no. 14)	0D	Solvothermal synthesis	2.11	28	19
7	[Co(dien)2]2[Sn2Se6]	Monoclinic	P21/n (no. 14)	0D	Solvothermal synthesis	N/A	50	20
8	[Co(dien)2]2[Sn2S6]	Monoclinic	P21/n (no. 14)	0D	Solvothermal synthesis	N/A	15	20
9	[Ni(dien)2]2[Sn2S6]	Monoclinic	P21/n (no. 14)	0D	Solvothermal synthesis	N/A	10	20
10	[(Ni0.4Zn0.6)(en)6] [Sn2Se6]	Monoclinic	P21/n (no. 14)	0D	Solvothermal synthesis	N/A	35	20
11	[(Mn1.67Zn0.33)(en)6] [Sn2Se6]	Monoclinic	P21/n (no. 14)	0D	Solvothermal synthesis	N/A	20	20
12	[Zn(tren)2H]SbSe4	Monoclinic	P21/n (no. 14)	0D	Solvothermal synthesis	2.07	7.25	21
13	[Ni(1,2-dap)3]2[Zn(1,2-dap)]Sb2Se8	Monoclinic	P21/n (no. 14)	0D	Solvothermal synthesis	1.95	9.75	21
14	[Zn(tren)]2Sb2Se5	Monoclinic	C2/c (no. 15)	0D	Solvothermal synthesis	2.26	1	22
15	[Zn(tepa)H]2Sb2S6	Tetragonal	I41/a (no. 88)	0D	Solvothermal synthesis	1.80	1	22
16	Mn(en)3Sb2S4	Monoclinic	P21/c (no. 14)	1D	Solvothermal synthesis	2.20	0.75	23
17	Co(en)3Sb2Se4	Monoclinic	P21/c (no. 14)	1D	Solvothermal synthesis	2.25	0.6	23
18	{[(Ga10S17)(H^+-AEP)2](H^+-AEP)2}	Orthorhombic	Pban (no. 50)	1D	Solvothermal synthesis	2.48	2.89	24
19	Ba3HgGa2S7	Monoclinic	P21/c (no. 14)	0D	Solid-state reaction	3.64	12.2	25
20	Ba2AgInS4	Orthorhombic	Pnma (no. 62)	2D	Solvothermal synthesis	1.98	0.02	26
21	[H3dien][Ag5Sn4Se12]·3H2O	Tetragonal	P4̄21m (no. 113)	3D	Solvothermal synthesis	1.82	109	27
22	[Cu2GeSe5]·[Mn(H^+en)2(en)]	Monoclinic	P21/c (no. 14)	1D	Solvothermal synthesis	1.69	0.78	28
23	[Cu2SnSe5]·[Mn(H^+en)2(en)]	Monoclinic	P21/c (no. 14)	1D	Solvothermal synthesis	1.49	3.83	28
24	(NH4)4Ag12Sn7Se22	Monoclinic	C2/c (no. 15)	3D	Solvothermal synthesis	1.21	40	29
25	BaAg2GeS4	Tetragonal	I4̄2m (no. 121)	3D	Solvothermal synthesis	2.21	2.25	26
26	Cs2CdGeSe4	Orthorhombic	Fddd (no. 70)	1D	Solvothermal synthesis	2.41	180	30
27	Cs2Hg2GeSe5	Tetragonal	I4 (no. 79)	0D	Solvothermal synthesis	1.92	65	30
28	Ba3Ag2Sn2S8	Cubic	I4̄3d (no. 220)	3D	Solvothermal synthesis	2.02	0.2	26
29	BaAg2SnS4	Orthorhombic	I222 (no. 23)	3D	Solvothermal synthesis	1.88	2.25	26
30	Cs2Ag2SnS4	Orthorhombic	Ibam (no. 72)	2D	Solvothermal synthesis	2.72	0.2	31
31	Cs2MnSnSe4	Orthorhombic	Fddd (no. 70)	2D	Solvothermal synthesis	1.90	45	32
32	Rb2MnSnSe4	Monoclinic	P21/n (no. 14)	2D	Solvothermal synthesis	1.61	80	32
33	K2HgSnSe4	Tetragonal	I4/mcm (no. 140)	1D	Solvothermal synthesis	2.01	1.74	33
34	Na6Cu8Sn3Se13	Cubic	Fm3̄c (no. 226)	3D	Solvothermal synthesis	1.76	3.32	33
35	Rb2AgAsS4	Triclinic	P1̄ (no. 2)	1D	Solvothermal synthesis	2.65	0.78	34
36	RbAg2AsS3	Triclinic	P1̄ (no. 2)	2D	Solvothermal synthesis	2.30	1.5	34
37	Cs2Ag6As2S7	Monoclinic	P21/m (no. 11)	2D	Solvothermal synthesis	2.10	3.83	34
38	Cs3CuAs4S8	Monoclinic	C2/c (no. 15)	2D	Solvothermal synthesis	2.26	5	35
39	Cs3CuAs4Se8	Monoclinic	C2/c (no. 15)	2D	Solvothermal synthesis	1.83	5	35
40	Cs2ZnAs4S8	Tetragonal	I41/a (no. 88)	3D	Solvothermal synthesis	2.24	3	36
41	Cs2CdAsSe5	Tetragonal	P42/n (no. 86)	0D	Solvothermal synthesis	2.06	4	37
42	[(NH4)Cs]CdAs4S8	Tetragonal	P4/n (no. 85)	2D	Solvothermal synthesis	2.36	0.75	36
43	AgCdAsS3	Monoclinic	C2/c (no. 15)	3D	Solid-state reaction	2.20	0.38	38
44	AgHgAsS3	Monoclinic	Cc (no. 9)	3D	Solid-state reaction	1.90	0.7	38
45	[pipH2]0.5[Ag2SbS3]	Monoclinic	P21/n (no. 14)	2D	Solvothermal synthesis	2.07	0.43	39
46	[pipH2]0.5[Ag2SbSe3]	Monoclinic	P21/n (no. 14)	2D	Solvothermal synthesis	1.95	0.495	39
47	Mn(tren)GaSbS4	Triclinic	P1̄ (no. 2)	1D	Solvothermal synthesis	2.08	7.5	46
48	Fe(tren)GaSbS4	Triclinic	P1̄ (no. 2)	1D	Solvothermal synthesis	1.62	3	46
49	[Mn(en)3]CdSb2S4	Monoclinic	C2/c (no. 15)	1D	Solvothermal synthesis	2.58	2.59	41
50	K3Mn2Sb3S8	Tetragonal	I4̄2m (no. 121)	3D	Solvothermal synthesis	1.61	7	42
51	Rb3Mn2Sb3S8	Tetragonal	I4̄2m (no. 121)	3D	Solvothermal synthesis	1.58	7	42
52	BaCuSbS3	Orthorhombic	Pbam (no. 55)	3D	Solvothermal synthesis	2.0	0.06	43
53	BaCuSbSe3	Orthorhombic	Pbam (no. 55)	3D	Solvothermal synthesis	1.6	0.03	43
54	Rb2ZnSb4S8	Triclinic	P1 (no. 1)	2D	Solvothermal synthesis	1.88	10	21
55	Rb2CuSb7S12	Triclinic	P1̄ (no. 2)	3D	Solvothermal synthesis	1.54	10	44
56	KCu2SbS3	Triclinic	P1̄ (no. 2)	2D	Reactive flux method	1.7	2.5	45
57	SrCuSbS3	Orthorhombic	Pbam (no. 55)	3D	Molten salt method	1.9	150	46
58	KCuZnS2	Tetragonal	I4/mmm (no. 139)	2D	Solvothermal synthesis	1.98	0.75	47
59	Ba2Cu2Cd2S5	Monoclinic	C2/m (no. 12)	2D	Solvothermal synthesis	2.21	0.40	48
60	Cs2ZnP2Se6	Triclinic	P1̄ (no. 2)	1D	Solid-state reaction	2.67	0.18	49
61	Lu5GaS9	Triclinic	P1̄ (no. 2)	3D	Solid-state reaction	2.34	0.15	50
62	Yb6Ga4S15	Monoclinic	C2/m (no. 12)	3D	Solid-state reaction	2.11	0.06	50
63	[(Ba19Cl4)(Ga6Si12O42S8)]	Orthorhombic	Cmcm (no. 63)	2D	Solid-state reaction	4.65	1.25	51
64	Zn4B6O12S	Cubic	I4̄3m (no. 217)	3D	Solid-state reaction	3.46	2.1	52
65	Sr2Sb2O2S3	Monoclinic	P21/c (no.14)	1D	Solid-state reaction	2.44	1.1	53
66	Sr2Sb2O2Se3	Monoclinic	P21/c (no. 14)	1D	Solid-state reaction	1.75	1.95	53
67	Sr6Cd2Sb6S10O7	Monoclinic	Cm (no. 8)	2D	Solid-state reaction	2.01	2.0	54

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2. Mechanism and measurement of photoelectric property

In 1887, the German physicist Heinrich Hertz first observed the photoelectric effect during experiments aimed at validating the wave theory of light. This groundbreaking discovery played a pivotal role in the development of quantum theory. In 1902, Wilhelm Lenard expanded on Hertz's findings, describing the photoelectric effect as a phenomenon in which electrons in metals absorb the energy of incident light and escape from the material's surface. However, this phenomenon could not be explained by the prevailing theories of that time. It wasn't until 1905 that Albert Einstein proposed his photon hypothesis, offering a clear and robust explanation for the photoelectric effect. According to Einstein, the photoelectric effect occurs when a semiconductor is bombarded by photons of energy (hv). The semiconductor absorbs this photon energy, leading to the generation of corresponding electrical effects.⁵⁵

Einstein's equation for the photoelectric effect, which encapsulates the energy transfer between light and electrons, is expressed as follows:

E_p = hv − W_s (1)

and Critical Frequency:

v₀ = W_s/h, (2)

hv: photon energy, W_s: metal surface work function, E_p = 1/2Mv²: the kinetic energy of photoelectron.

When a photon strikes the surface of a semiconductor, its energy is transferrs to an electron in the material. This energy helps the electron overcome the attractive forces of the metal surface, allowing it to escape. The remaining energy is then converted into the kinetic energy of the emitted photoelectron. The photocurrent, which is generated by the absorption of light energy, results from the excitation of electrons and holes within the material. Upon absorption, electrons in the semiconductor transition from the valence band to the conduction band. The generated charge carriers then move towards the surface of the semiconductor. If an external circuit is connected, this movement of charge carriers results in the flow of an electric current. The photocurrent density is defined as the ratio of the photocurrent to the illuminated area of the photoelectrode under a specific light source, and it is a critical parameter for evaluating the photoelectric effect in photoelectrochemical experiments.

In photoelectric response experiments, the standard three-electrode system is commonly used, and these experiments are typically conducted on an electrochemical workstation. The semiconductor powder is coated onto indium tin oxide (ITO) glass, which serves as the working electrode. The reference electrode is usually a saturated mercury/mercury chloride (Hg/HgCl₂) or silver/silver chloride (Ag/AgCl₂) electrode, while a platinum (Pt) electrode is commonly employed as the counter electrode. The electrolyte solution is typically a standard aqueous Na₂SO₄ solution, which provides the necessary ionic conductivity for the system. The photocurrent density, a key parameter in photoelectric experiments, can be expressed using the following equation:

J_p = j_max × (η_abs × η_sep × η_inj) (3)

J_p: actual measured photocurrent density, j_max: the maximum theoretical photocurrent density of a semiconductor photoelectrode, η_abs: light absorption efficiency of semiconductor photoelectrode, η_sep: charge separation efficiency of semiconductor photoelectrode, η_inj: surface charge injection efficiency of semiconductor photoelectrode.⁵⁶

In parallel, the photoelectric conversion efficiency can be quantified using the following formula:

J_p: photocurrent density, J_d: dark current density, λ: incident monochromatic light wavelength, P₀: incident light intensity on the surface of the photoelectrode.⁵⁷

From eqn (3) and (4), it is evident that the photoelectric conversion efficiency (η) is directly proportional to the photocurrent density (J_p). This photocurrent density, in turn, is influenced not only by the light absorption and utilization efficiency of the photoelectrode, but also by the separation efficiency of the photogenerated charge carriers both internally and at the interface. The latter is a crucial factor in determining the photoelectrochemical properties of the system. The transient photocurrent response is an important tool for evaluating the separation efficiency of photo-induced electron–hole pairs within the photoelectrode. A higher photocurrent typically indicates a more efficient separation of these charge carriers. The process of photoelectrochemical conversion involves the absorption of light by semiconductor materials, which excites electrons (or holes) and drives them to participate in chemical reactions, leading to the formation of new substances. This process is influenced by multiple factors, including the semiconductor's ability to capture light, the generation and migration of photogenerated charge carriers, and the catalytic reactions occurring at the surface of the photoelectrode. Each of these factors plays a significant role in determining the overall efficiency of photoelectric conversion and, by extension, the performance of the photoelectrode in generating current and facilitating chemical transformations.

The photocurrent tests in this review are most taken using three-electrode mode in Na₂SO₄ aqueous solution under 300 W Xe simulated visible light with λ ≥ 420 nm. However, it is a common phenomenon that different compounds are tested under distinct bias voltages in the range of about 0–1.0 V. Generally, higher bias voltage brings larger photocurrent density value, because higher potential can restrain carrier trapping effect induced by interface defects through the induced electric field and thus retard the recombination rate of electrons and holes.^53,54

3 Crystal structures and band gaps of main group chalcogenidometalates

3.1 Crystal structures of main group chalcogenidometalates with binary anionic frameworks

The common main group metals that constitute chalcogenides include Ga and In from group 13, Ge and Sn from group 14, and As and Sb from group 15. These metals predominantly form anion structures with chalcogen elements such as S or Se. In the presence of templating agents like organic amines, ammonium salts, or surfactants, the main group metals are coordinated with S or Se atoms, resulting in the formation of polymeric ions. When the coordination ability of these oligomeric metal ions is limited, charge balancing is achieved by incorporating cationic clusters. These clusters are typically composed of TM-based ions and organic molecules, leading to the creation of organic-hybrid compounds with a binary anionic framework. These compounds generally exhibit a 0D cluster structure and possess remarkable optical and photoelectric properties.

3.1.1 Crystal structures of group 14 chalcogenidometalates (Ge, Sn) with binary anionic frameworks. The BBUs of Ge/Sn-chalcogenides are typically the tetrahedral [MQ₄] unit, where M represents Ge or Sn, and Q denotes S or Se. In the presence of templating agents such as organic amines, ammonium salts, or surfactants, these tetrahedral [MQ₄] units can aggregate to form polytetrahedral structures, denoted as [M_xQ_y]^z−, through μ-Q²⁻ bridging bonds. These units can link via corner-sharing or edge-sharing interactions, resulting in a wide variety of hybrid chalcogenidometalates with diverse dimensionalities and structural configurations. Recent studies have highlighted a significant correlation between the basic structural motifs of Ge/Sn-chalcogenides and their photoelectric properties, suggesting that the arrangement and connectivity of the [MQ₄] units play a crucial role in determining the performance of these materials in optoelectronic applications.

According to H. Luo et al. (2015), five hybrid main-group chalcogenides—[Mn₂(en)₄Ge₂S₆]_n (1), [Mn₂(dap)₄Ge₂S₆]_n (2), [V(en)₂(ea)]₂[Ge₂Se₆] (3), [V(teta)(ea)]₂[Ge₂Se₆] (4), and [V₂(en)₆(μ-O)][Ge₂Se₆] (5)—were synthesized via a solvothermal method.¹⁸ In compounds 1 and 2, the dimeric [Ge₂S₆]⁴⁻ anions form 1D chain-like structures, where the Mn-containing complex cations are interconnected with the anions (Fig. 2a and b). Compounds 3 and 4 are based on [Ge₂Se₆]⁴⁻, where two [GeSe₄] units are connected by edge-sharing, with V-containing complex cations completing the structures (Fig. 2c and d). The cation in compound 5 is [V₂(en)₆(μ-O)]⁴⁺, with ethylenediamine (en) acting as a monodentate ligand (Fig. 2e). Notably, compounds 3–5 exhibit excellent photocurrent responses, demonstrating their potential as efficient photosensitizers. The rare low-valent V²⁺ complex cation selenide, [V(dien)₂]₂[Sn₂Se₆]₂⁴⁻ (6), which contains [Sn₂Se₆]⁴⁻ anions and [V(dien)₂]²⁺ complex cations (Fig. 2f), shows a reproducible photocurrent response of approximately 2.0 μA cm⁻².¹⁹ This suggests that photo-generated electrons from the Se-4p orbitals can rapidly transfer to the FTO electrode, generating an anodic current. The UV–Vis absorption data for compound 6 (Table 1) indicates an experimental band gap of 2.11 eV, further supporting its photocurrent-generating potential. 1–2 show very low responsiveness in comparison with that of 4–6. This result means that 4–6 could be a good photosensitizer.

Fig. 2 The crystal structure of compounds 1–6 (a–f).

Additionally, the photocurrent responses of five novel isostructural TM–Sn–Q 0D cluster structures (TM = transition metals; Q = S, Se) (7–11), reported by Menghe Baiyin in 2022, are both rapid and repeatable.²⁰ Among these, [Co(dien)₂]₂[Sn₂Se₆] (7) exhibits a current density of nearly 50 μA cm⁻², which surpasses that of most chalcogenidostannates, indicating superior electron–hole pair generation and separation efficiency. These findings suggest that chalcogenidostannates containing transition metal based complexes may exhibit enhanced photocurrent responses compared to other chalcogenides (see subsequent chapters). This improvement may be attributed to the decrease in atomic radius of group 14 elements across the period, as well as the corresponding reduction in electronegativity, which facilitates the migration of more free electrons into the external circuit, thereby producing a larger photocurrent. Moreover, TM-based complexes contribute to the formation of unusual structures through their unique spatial arrangements, providing synergistic effects with the inorganic frameworks.

3.1.2 Crystal structures of group 15 chalcogenidometalates (As, Sb) with binary anionic frameworks. In comparison to the group 14, metal elements from the group 15 of the periodic table often exhibit a broader range of coordination modes, owing to the presence of stereochemically active lone pairs. These lone pairs contribute to the flexibility and diversity in the coordination environment of these elements.⁵⁸ The anionic frameworks of binary group 15 chalcogenidometalates are primarily composed of a series of polymeric ions, [M_xQ_y]^z− (M = As, Sb; Q = S, Se). These frameworks are formed by [MQ₃] trigonal and [MQ₄] tetrahedral units, which serve as the BBUs of the structure. These unique coordination motifs not only influence the structural characteristics of these compounds but also have a significant impact on their physical properties. According to existing studies, photoresponsive characterizations have predominantly been carried out on chalcogenides that incorporate inorganic–organic hybrid cations. For instance, the 0D [Zn(tren)₂H]SbSe₄ (12) comprises trigonal bipyramidal Zn²⁺ ions and [SbSe₄] clusters, while the unique [Ni(1,2-dap)₃]₂Zn(1,2-dap)Sb₂Se₈ (13) features Zn²⁺ ions that coordinate with both organic amines and Se atoms (Fig. 3a and b).²¹ In 2023, two novel chalcogenides were synthesized incorporating [Zn(tren)]²⁺ and [Zn(tepa)H]²⁺ cations. These materials showcase 0D cluster structures based on the binary anionic frameworks [Sb₂Se₅]_n²ⁿ⁻ and [Sb₂S₆]_n³ⁿ⁻, respectively, both of which are built from the primary [SbQ₄] (Q = S, Se) unit (Fig. 3c and d).²² Additionally, the same research group solvothermally synthesized Mn(en)₃Sb₂S₄ (16) and Co(en)₃Sb₂Se₄ (17), which are composed of Mn/Co complex cations and 1D anionic chains (Fig. 3e).²³

Fig. 3 The structure of compounds 12 (a), 13 (b), 14 (c), 15 (d), and 16 (e) (16 and 17 are isostructural).

Among these compounds, 12 and 13 exhibit notably stronger photocurrent responses compared to others, indicating superior photogenerated electron–hole pair transfer and separation efficiency. The enhanced activity of the lone pair electrons of Sb³⁺ in compounds 12 and 13 contributes to a redshift in the ultraviolet absorption edge, thereby reducing the band gap. A narrower band gap allows for a broader spectral absorption range and a higher absorption rate across the solar spectrum, ultimately leading to the generation of more photogenerated charge carriers, which significantly enhances the photoconductivity effect. It indicated that compound 12 and 13 have a potential development prospect in the field of solar cell materials.

3.2 Crystal structures of main group chalcogenidometalates with ternary anionic frameworks

The incorporation of transition metals into the anionic frameworks of main group chalcogenidometalates significantly enhances their structural complexity and imparts distinctive properties, sparking considerable interest in their study. Compared to chalcogenidometalates with simpler binary anionic frameworks, the introduction of ternary mixed anions leads to more intricate polyhedral distortions. These distortions not only contribute to the development of stronger polarity but also induce greater anisotropy in the materials. As a result, ternary anion frameworks often exhibit exceptional photoelectronic properties. This is attributed to the combination of metal atoms with varying sizes and electronegativities, which creates a rich interplay of electronic states and structural variations that can be finely tuned for specific applications.

3.2.1 Crystal structures of group 13 chalcogenidometalates (Ga, In) with ternary anionic frameworks. The basic building unit of Ga/In chalcogenides is the tetrahedral [MQ₄] unit (M = Ga, In; Q = S, Se). Under solvothermal conditions, and in the presence of templating agents such as organic amines, quaternary ammonium salts, or other nitrogen-containing organic compounds, multiple [MQ₄] tetrahedra can aggregate into larger polytetrahedral structures, forming [M_xQ_y]^z− clusters. These clusters can exhibit various topologies, such as hypertetrahedral clusters (T_n clusters), pentagonal supertetrahedral clusters (P_n clusters), hatched supertetrahedral clusters (P_n clusters), and other complex supertetrahedral configurations. The formation of these diverse superclusters allows for the synthesis of a wide range of inorganic–organic hybrid materials and inorganic chalcogenidometalates with varying dimensionalities, spanning from 1D to 3D architectures. For instance, in the 1D structure {[(Ga₁₀S₁₇)(H⁺-AEP)₂](H⁺-AEP)₂} (18), a T₃-[GaS] cluster is coordinated to two organic AEP ligands through neutral amine groups that bond to two corner Ga atoms, forming a unique molecular assembly (Fig. 4a).²⁴ In contrast, the 0D Ba₃HgGa₂S₇ (19) features Ba²⁺ counterions, and the anionic framework displays a [Ga₂S₂] parallelogram formed between two [GaS₄] tetrahedra, which further links to the [Hg₂Ga₄S₁₄]¹²⁻ string (Fig. 4b).²⁵ Moving to the two-dimensional Ba₂AgInS₄ (20), the structure is built from [AgS₄] and [InS₄] tetrahedra that are connected through corner-sharing interactions, resulting in a layered 2D framework (Fig. 4c).²⁶

Fig. 4 The structure of compound 18 (a), 19 (b) and 20 (c).

Among these ternary chalcogenides, Ba₃HgGa₂S₇ (19) demonstrates the strongest photocurrent response, reaching approximately 12.2 μA cm⁻² (Table 1). The enhanced photocurrent response can be attributed to the presence of [HgS₂] units within the structure, where the large polarizable Hg atoms—due to their fully occupied d¹⁰ configuration—contribute to the formation of built-in electric fields via Jahn–Teller distortion.⁵⁹ This phenomenon promotes efficient photogenerated charge separation, stabilizes in-plane carriers, and reduces the formation of photogenerated carrier complexes, which collectively enhance the photocurrent response. UV-Vis absorption spectra reveal distinct band gaps for the materials: 2.48 eV for compound 18, 3.64 eV for compound 19, and 1.98 eV for compound 20 (Table 1). Notably, compound 19 exhibits the largest band gap, which is likely due to its unique chemical composition and electronic structure. The [HgS₂] units within Ba₃HgGa₂S₇ (19) primarily contribute to the valence band, resulting in a relatively wide band gap. However, 19 exhibits a stronger photocurrent response compared to the other two compounds, which further illustrates the significant impact of large polarizable Hg atoms on photocurrent property. Therefore, 19 provides an opportunity for discovering new chalcogenides with promising photocurrent properties.

3.2.2 Crystal structures of group 14 chalcogenidometalates (Ge, Sn) with ternary anionic frameworks. As outlined in section 3.1.1, the BBUs of Ge/Sn-chalcogenidometalates are the tetrahedron [MQ₄] (where M = Ge, Sn and Q = S, Se). A series of polymeric thio/selenidogermanates with ternary anionic frameworks, which exhibit stability in air, have been synthesized by incorporating transition metals as linkers for the [SnQ₄] units. A representative compound featuring protonated organic amine cations is the organic–inorganic silver-rich selenidostannate [H₃dien][Ag₅Sn₄Se₁₂]·3H₂O (21) (Fig. 5a).²⁷ The core structure of compound 21 comprises discrete [Sn₂Se₆] clusters and [Ag₅Se₈]_n chains, which interconnect to form a 3D [Ag₅Sn₄Se₁₂]_n³ⁿ⁻ framework with 1D channels running through it. Similar to compound 21, two isostructural compounds, [Cu₂MSe₅]·[Mn(H⁺-en)₂(en)] (M = Ge (22), Sn (23)), feature 1D chains of [Cu₂MSe₅]⁴⁻ anions, and their band gaps were found to be 1.69 eV for compound 22 and 1.49 eV for compound 23 (Fig. 5b).²⁸ The near-infrared-triggered photoelectric response observed in compound 23 highlights its potential for application in photoelectric sensors. Compared to compounds 21 and 22, the band gaps of compounds 23 and (NH₄)₄Ag₁₂Sn₇Se₂₂ (24) display a notable red shift (1.49 and 1.21 eV, respectively), suggesting their potential for near-infrared photoelectronic applications (Table 1).²⁹ Additionally, the photocurrent response demonstrates highly repeatable photovoltage behavior, further validating the near-infrared photoelectronic capabilities of compounds 23 and 24. Compound 21, in particular, exhibits a rapid and stable photocurrent response with a current intensity as high as 109 μA cm⁻², indicating highly efficient carrier separation under light irradiation. Data suggests that, in most cases, tin selenides exhibit superior photocurrent responses compared to germanium selenides, as the heavier Sn atom typically results in a lower conduction band energy, which is more favorable for charge carrier movement.²⁸

Fig. 5 The structure of compound 21 (a), 23 (b) and 24 (c). (22 and 23 are isostructural).

Inorganic multi-compounds involving alkali or alkaline earth metals as equilibrium cations filling the ternary germanium/tin-anion frameworks have also been explored. In the case of BaAg₂GeS₄ (25),²⁶ the 3D anionic [Ag₂GeS₄]²⁻ framework consists of [AgS₄] tetrahedra and an infinite [AgS₂] layer, where Ge⁴⁺ ions are embedded between the AgS2 layers, sharing corners with the [AgS₄] tetrahedra (Fig. 6a). Other noteworthy examples include Cs₂CdGeSe₄ (26) and Cs₂Hg₂GeSe₅ (27), both synthesized under solvothermal conditions.³⁰ Compound 26 is composed of 1D infinite chains of {[GeCdSe₄]²⁻} anions, which consist of [GeSe₄] and [CdS₄] tetrahedra (Fig. 6b). Compound 27, on the other hand, features a 0D cluster structure where four [HgSe₄] tetrahedra form an 8-membered ring via vertex-sharing. This 8-membered ring contributes to the formation of [GeHgSe₅]_n²ⁿ⁻ clusters in conjunction with [GeSe₄] tetrahedra (Fig. 6c). As shown in Table 1, the band gap (E_g) of compound 27 is smaller than those of compounds 25 and 26, suggesting a broader absorption range. The photocurrent densities for compounds 25, 26, and 27 are 0.02, 180, and 65 μA cm⁻², respectively, indicating that compounds 26 and 27 exhibit significantly better photoelectron-hole transfer and separation efficiency than compound 25. These results support the idea that transition metals with a d¹⁰ electron configuration in the anion skeletons can enhance photocurrent response properties, as discussed in section 3.2.1.

Fig. 6 The structure of compounds 25 (a and d), 26 (b and e), and 27 (c and f).

In the category of A–Ag–Sn–S compounds, Ba₃Ag₂Sn₂S₈ (28) features a 3D [A_g2Sn₂S₈]⁶⁻ framework constructed by [AgS₄] and [SnS₄] units through vertex-sharing (Fig. 7a).²⁶ BaAg₂SnS₄ (29)¹⁶ and Cs₂Ag₂SnS₄ (30)²¹ both possess outstanding optical performance. For 29, vertex-sharing of [AgS₄] tetrahedra help form the [AgS₂] 2D layer, while Sn tetrahedra connect [AgS₂] layers and build a 3D [Ag₂SnS₄]²⁻ skeleton (Fig. 7b). For compound 30, [AgS₂]_n³ⁿ⁻ chains which formed by [AgS₄] tetrahedra are connected via Sn⁴⁺ ions and generating a 2D layered anion (Fig. 7c). The different structural dimensions of 29 and 30 mainly due to the types of charge-balancing agent. Among the A–Ag–Sn–S compounds, the photocurrent density of 29 (2.25 μA cm⁻²) indicates a good transfer and separation efficiency of photogenerated electron–hole pairs under simulated solar light illumination, which may be related to its E_g of 1.88 eV (Table 1). Band gap plays an important role in photocurrent response. When a certain compound has a smaller band gap, it is easier for electrons to transition across the band gap, resulting in more electrons and holes, enhancing the photocurrent activity. The good photoelectric responsive properties of compound 29 under simulated solar light illumination make it promising as a photoelectric device.

Fig. 7 The structure of compounds 28 (a and d), 29 (b and e), and 30 (c and f).

Typical examples of tin-selenides include the family of A₂TSnSe₄ (A = alkali metal; T = Mn, Hg). Recent work on the photocurrent response performances of Cs₂MnSnSe₄ (31) and Rb₂MnSnSe₄ (32) supported that the tin-selenides had a strong photocurrent response.³² For compound 31, edge-sharing occurs between [MnSe₄] and [SnSe₄] to form the 1D anionic chain [MnSnSe₄]_n²⁻ (Fig. 8a). The structure of 32 features 2D [MnSnSe₄]_n²⁻ anionic network, which is composed of [Mn₂Sn₂Se₁₀] cluster connected with four other adjacent units (Fig. 8b). Furthermore, it is clear that the charge-balanced Rb⁺/Cs⁺ are both located between the anions. The E_g of 31 and 32 are 1.90 eV and 1.61 eV, respectively (Table 1). The photocurrent densities of 31 and 32 are 45 μA cm⁻² and 80 μA cm⁻², indicating two p-type semiconductors. The narrow bandgap and high photocurrent response make compound 32 an alternative material for solar cells. Another example in the family of A₂TSnSe₄ (A = alkali metal; T = Mn, Hg) is K₂HgSnSe₄ (33), which features 1D [HgSnSe₄]_n²ⁿ⁻ anions but a much weaker photo response (1.74 μA cm⁻²), close to that of Na₆Cu₈Sn₃Se₁₃ (34) (3.32 μA cm⁻²) contains 3D [Cu₈Sn₃Se₁₃]⁶⁻ anionic framework which balanced by Na⁺ ions (Fig. 8c and d).³³ A conclusion can be drawn through the research of the A₂TSnSe₄ (A = alkali metal; T = Mn, Hg) family that crystal structure has a vital influence on optical properties and photocurrent response properties of compounds.

Fig. 8 The structure of compounds 31 (a and e), 32 (b and f), 33 (c and g) and 34 (d and h).

3.2.3 Crystal structures of group 15 chalcogenidometalates (As, Sb) with ternary anionic frameworks. The basic building unit of thio/selenidoarsenates(V) is mainly tetrahedral [AsQ₄]³⁻ (Q = S, Se), which is usually linked to transition metal polyhedra via edge/vertex-sharing to form compounds with a variety of structures. In 1D Rb₂AgAsS₄ (35),²⁴ the As⁵⁺ ion coordinated with four S²⁻ ions in a nearly ideal tetrahedral configuration and formed a [AgAsS₄]²⁻ dimer unit with AgS₄ distorted tetrahedra as found in Fig. 9a. Trivalent thio/selenidoarsenates(III) mainly adapt to the trigonal pyramid [As^IIIS₃] unit. In the 2D layered structure of RbAg₂AsS₃ (36),³⁴ the [As^IIIS₃] unit is stabilized by connecting with [AgS₄]. Cs₂Ag₆As₂S₇ (37) also possesses a 2D anionic layer with corner-sharing [As^IIIQ₃] and [AgS₃] units and the mono-layered [Ag₃AsS₄]_n²ⁿ⁻ form a double-layered structure via the connection of S²⁻ ions (Fig. 9c).³⁴ The photocurrent responses of 35–37 enhance along with their E_g values decreasing from 2.65 to 2.10 eV. According to the density of states (DOS) calculation by density functional theory (DFT), valence bands of 35–37 are mainly composed of Ag-4d and S-3p states, but due to the valence change of As ion, As⁵⁺ with unoccupied 4s states in 35 causes the predomination of As-4s and S-3p states in conduction band bottom, while As³⁺ with filled 4s orbitals in 36 and 37 causes the predomination of As-4p and S-3p states in conduction band bottom. Thus, band structure changes caused by As⁵⁺/As³⁺ ions affected the photocurrent responses of the compounds. Moreover, the increasing of Ag/As ratios of 35–37 indicated that a higher proportion of Ag⁺ can improve the photocurrent responses through adjusting band structure.

Fig. 9 The structure of compounds 35 (a and d), 36 (b and e), and 37 (c and f).

As displayed in Fig. 10a, Cs₃CuAs₄Q₈ (Q = S, Se) (38, 39)³⁵ 2D layer structure was formed by eight [AsQ₃] and two [CuQ₃] units, which connected to form a [Cu₂As₈Q₁₈] cluster through vertex-sharing. These [Cu₂As₈Q₁₈] clusters are interlinked to construct a double-layered 2D [CuAs₄S₈]³⁻ anion. The open structure of a double-layered anion provides enough space for 4 independently located Cs⁺ cations (Fig. 10a). 3D Cs₂ZnAs₄S₈(40) compound was obtained by replacing the transition metal Cu by Zn, which is constructed by Cs⁺ cations, [ZnS₄] tetrahedra, and 1D [As₄S₈]⁴⁻ chains consist of corner-sharing [As₄S₉] groups (Fig. 10b).³⁶ The structure of Cs₂CdAsSe₅(41) is formed of windmill-like [Cd₄As₄Se₁₆(Se₂)₂]⁸⁻ clusters and charge balancing Cs⁺ cations (Fig. 10c).³⁷ The crystal structure of [(NH₄)Cs]CdAs₄S₈ (42) is composed of regular [CdS₄] and tetranuclear [As₄S₈] clusters, the BBUs form the two-dimensional [CdAs₄S₈]²⁻ layer filled with the dispersed (NH₄)⁺ or Cs⁺ ions (Fig. 11a).²⁶ The above anions of four thio/selenidoarsenates(III) possess an identical stoichiometry of 1–4–8, but they are significantly distinct in structural features from 3D to 0D while the photocurrent responses (Table 1) of 38–41 occur in a narrow range from 0.75 to 5 μA cm⁻², indicating that the anion dimension has little influence on their photocurrent responses. Nevertheless, selenides 39 and 41 still display better photocurrent response properties and narrower band gaps than the other three sulfides.

Fig. 10 The structure of compounds 38 (a and d), 40 (b and e), and 41 (c and f). (38 and 39 are isostructural).

Fig. 11 The structure of compounds 42 (a), 43 (b), 44 (c), 45 (d), 47 (e), and 49 (f). (45 and 46 are isostructural, 47 and 48 are isostructural).

Double d¹⁰ cations with a variety of different coordination modes could be introduced to obtain thioarsenites AgMAsS₃ (M = Cd, Hg) (43, 44). In these two compounds, the building units contain d¹⁰ cations are [AgS₄]/[HgS₄] in AgHgAsS₃ (Fig. 11c) and [AgS₅]/[CdS₆] in AgCdAsS₃ (Fig. 11b), respectively.³⁸ The non-centrosymmetric (NCS) AgHgAsS₃ show stronger photocurrent responses compared to centrosymmetric (CS) AgCdAsS₃, which indicates that built-in electric field generated by polar structure could be beneficial for photogenerated electrons/holes separating. Meanwhile, the smaller band gap of AgHgAsS₃ helps absorb a wider range of light.

The first-principles calculations of density of states elaborate the valence band of 44 mainly contains Ag-4d and S-3p states and shows strong stereochemical lone-pair activity. The conduction band bottom is composed of As-4p, S-3p, and Hg-5d states. Other reported trivalent thio/selenidoarsenates(III) such as RbAg₂AsS₃ (36), Cs₂Ag₆As₂S₇ (37), Cs₂ZnAs₄S₈ (40) and [(NH₄)Cs]CdAs₄S₈ (42) etc. exhibit the same feature of the band structure. Therefore, the essential motifs which dictates the band gap of AgHgAsS₃ are distorted [HgQ₄] (Q = S, Se) and [AsQ₄] (Q = S, Se) units, in which charge-balancing cations are rarely involved.

The transition metals (Cu⁺, Ag⁺, Cd²⁺, Hg²⁺) can further integrate with [SbS₃] units in thioantimonates to build the TM–Sb–Q (Q = S, Se) ternary anions. A series of organic hybrid thioantimonates with ternary anionic frameworks, which are stable in air, have been obtained by using transition metals as linkages for the [SbS₃] units. [pipH₂]_0.5[Ag₂SbS₃] (45)³⁹ has a 2D layered structure and it is isostructural with [pipH₂]_0.5[Ag₂SbSe₃] (46) (Fig. 11d).³⁹ Compounds Mn(tren)GaSbS₄ (47)⁴⁰ and Fe(tren)GaSbS₄ (48)⁴⁰ are also isostructural, which featured a 1D chain formed by the pyramidal [SbS₃] unit and slightly distorted tetrahedral [GaS₄] unit (Fig. 11e). However, these isostructural compounds exhibit different photocurrent densities due to their band structure and carrier separation efficiency. In addition, [Mn(en)₃]CdSb₂S₄ (49)⁴¹ features 1D anionic chains and [Mn(en)₃]²⁺ charge-balancing complex cations (Fig. 11f).

By directly introducing alkali metal as the structure-directing agent, the novel Mn-based thioantimonate A₃Mn₂Sb₃S₈ (A = K, Rb) (50, 51)⁴² which belongs to the non-centrosymmetric space group were reported. Both compounds exhibit unique 3D open frameworks constructed by [Mn₈S₃₂] and [Sb₃S₇] units (Fig. 12a) and display the same rapid and consistent photocurrent responses, which indicate that the charge-balanced cations rarely affect the E_g and photocurrent responses. Other quaternary thioantimonates exhibit photocurrent response properties are BaCuSbS₃ (52), BaCuSbSe₃ (53) (Fig. 12b),⁴³ Rb₂ZnSb₄S₈ (54) (Fig. 12c),²¹ and Rb₂CuSb₇S₁₂ (55)⁴⁴ which featured a 3D or 2D framework with [CuS₃] and [SbS₃] triangular pyramids (Fig. 12e), and KCu₂SbS₃ (56)⁴⁵ with the layered structure of two single heavily distorted graphene-like layers based on the [Cu₂SbS₃]⁻ building unit (Fig. 12f). Another important example is SrCuSbS₃ (57) (Fig. 12d),⁴⁶ which is isostructural with 52 and 53, and consists of 3D [CuSbS₃]²⁻ extended framework and Sr²⁺ ions with E_g of 1.91 eV. When Sr²⁺ ions are partially replaced by Pb²⁺ ions, the E_g can be decreased to 1.63 eV, and the largest photocurrent density was tested as 162.9 μA cm⁻² at 3 V for Sr_0.85Pb_0.15CuSbS₃. Pb²⁺ doping decreased the E_g of SrCuSbS₃ and created excellent solar light absorption photocatalytic materials. Compared to that of ionic Sr–S bonds in SrCuSbS₃, the more delocalized electrons of Pb–S bonds efficiently narrow the E_g of the doping compounds. In addition, the introduction of Pb-6s/6p states around the Fermi level provides photo-generated electrons/holes separation and transport with enough mobility in optoelectronic processes.

Fig. 12 The structure of compounds 50 (a), 52 (b), 54 (c), 55 (e), 56 (f), and 57 (d). (50 and 51 are isostructural, 52 and 53 are isostructural).

4 Crystal structures and band gaps of other special chalcogenides

Multinary transition metal sulfides are renowned for their rich structural diversity and remarkable physical and chemical properties, which primarily arise from the various coordination modes they can adopt with S²⁻ ions.⁶⁰ However, the photocurrent response properties of transition metal chalcogenides remain relatively underexplored. Among the existing studies, we have identified several chalcogenides incorporating transition metals, whose anionic frameworks are predominantly 2D in nature, and these materials exhibit excellent photocurrent response characteristics. Typically, transition metal ions such as Zn²⁺ and Cd²⁺ exhibit coordination environments that include trigonal pyramidal [ZnS₄] and octahedral [ZnS₆] motifs. In particular, the compound KCuZnS₂ (58)⁴⁷ (Fig. 13a) presents an intriguing case, where both Cu⁺ and Zn²⁺ ions occupy the same crystallographic site. In this structure, each [CuS₄] and [ZnS₄] tetrahedron is connected to the other units via edge-sharing, resulting in a unique 2D layered arrangement. Similarly, another compound, Ba₂Cu₂Cd₂S₅ (59)⁴⁸ (Fig. 13b), features a layered anionic framework of [Cu₂Cd₂S₅]⁴⁻, with Cd²⁺ ions coordinated in tetrahedral geometry. Both of these compounds exhibit rapid and consistent photocurrent response profiles, indicating their strong potential for optoelectronic applications. The experimentally determined E_g of compounds 58 and 59 are 1.98 eV and 2.21 eV, respectively (Table 1). These values suggest that these materials are promising candidates for use in photoelectric devices, where their photocurrent response properties are of paramount importance. In our view, there is a critical need to develop and explore new transition metal chalcogenides with superior photocurrent response properties to further advance the field of energy conversion and optoelectronics.

Fig. 13 The structure of compounds 58 (a) and 59 (b).

In addition to the compounds discussed earlier, recent studies have revealed that certain chalcogenide systems with unique structures exhibit notable photocurrent properties. The crystal structure of Cs₂ZnP₂Se₆ (60)⁴⁹ is illustrated in Fig. 14. It features a 1D chain structure composed of [ZnP₂Se₂]²⁻ chains that extend along the c-axis, interspersed with Cs⁺ cations. Two types of ethane-like motifs are observed, where the [P₂Se₆]⁴⁻ groups and the [ZnSe₄]⁶⁻ units, which have four distinct bond lengths, intersect and share Se atoms, forming the 1D [ZnP₂Se₂]²⁻ anionic chain. The optical absorption properties of the material are primarily governed by transitions between the valence band and conduction band near the Fermi level. Thus, the contributions of the [ZnSe₄] and [P₂Se₆] groups are crucial to the material's optical characteristics. Compound Lu₅GaS₉ (61),⁵⁰ shown in Fig. 15a, has the highest rare-earth (RE)/Ga molar ratio reported thus far in the RE/Ga/S system. All Lu atoms are six-fold coordinated in distorted [LuS₆] octahedra. Remarkably, discrete dimeric [(GaS₄)₂] tetrahedra serve as the central species in the 3D anionic Lu–S channels. This structure plays a pivotal role in the material's photocurrent response. In Fig. 15b, Yb₆Ga₄S₁₅ (62)⁵⁰ features a distinct 3D framework based on 2D Yb–S layers, which are composed of two different corner-sharing substructures. These layers are further interconnected by 1D [GaS₄] double-tetrahedron chains extending along the c-axis. Both compounds exhibit high efficiency in transferring photo-generated electrons and in separating electron–hole pairs. However, compound 61 demonstrates an even stronger transient photocurrent response, approximately three times larger than that of compound 62.

Fig. 14 The structure of compounds 60.

Fig. 15 The structure of compounds 61 (a) and 62 (b).

Recently, oxychalcogenides with mixed-anion groups have attracted significant attention as an important class of optoelectronic functional materials.⁶¹ This is due to their ability to combine the beneficial properties of oxides and chalcogenides through a chemical substitution strategy.⁶² As shown in Fig. 16a, compound [(Ba₁₉Cl₄)(Ga₆Si₁₂O₄₂S₈)](63),⁵¹ features a unique architecture in which two [GaO₂S₂], four [GaO₃S], and four [Si₂O₇] units apex-share to form a [Si₈Ga₆O₃₂S₈] circular cluster. These clusters are interconnected to form a 2D wavelike layer along the ac-plane, facilitated by a disordered [Si₂O₇] unit that shares corners with O atoms. Between these layers, discrete Ba²⁺ cations and Cl⁻ anions occupy interstitial spaces. Notably, compound 63 represents the first heteroanionic chalcogenide to exhibit a photocurrent response, marking a significant breakthrough in the field. Subsequently, other oxychalcogenides, including Zn₄B₆O₁₂S (64),⁵² Sr₂Sb₂O₂Q₃ (Q = S (65), Se (66))⁵³ and Sr₆Cd₂Sb₆S₁₀O₇ (67)⁵⁴ have been found to exhibit photocurrent responses. Compound 64 crystallizes in the noncentrosymmetric cubic structure. As shown in Fig. 16b, twenty-four vertex-sharing [BO₄]⁵⁻ tetrahedra form a sodalite cage, while four [ZnSO₃]⁶⁻ tetrahedra containing Zn–O and Zn–S bonds inside the cage, help restricting the rotation of rigid [BO₄]⁵⁻ tetrahedra. Compounds 65 and 66, show in Fig. 16c, adopt structures composed of double chains of edge-sharing [SbSe₄O] square-based pyramids. In Fig. 16d, compound 67 exhibits the polar space group Cm with ²_∞[CdSb₂OS₅]⁴⁻ layers composed of [CdS₃]⁴⁻ tetrahedra and tetragonal pyramids of antimony [SbOS₂]³⁻/[SbS₃]³. The pseudochains built from [SbO₄]⁵⁻ units fill the spaces between the layers as well as Sr²⁺. Among these oxychalcogenides, compound 64 generate the highest photocurrent response (2.1 μA cm⁻²) with a relatively wide band gap of 3.46 eV, which is inconsistent with the general trend that narrower band gap always brings better photocurrent response. The same result occurs in 63 (∼1.25 μA cm⁻², 4.65 eV). The special coordination environments of cations in these structures, namely the cations bond with both O²⁻ and Q²⁻, contribute to the formation of polar units and thus the built-in electric field, can enhance the efficiency of e⁻/h⁺ separation. Therefore, these oxychalcogenides emerge as potential photocatalysts, offering improved photocurrent responses under visible light or ultraviolet illumination compared to oxides.

Fig. 16 The structure of compounds 63 (a), 64 (b), 65 (c) and 67 (d). (65 and 66 are isostructural).

5 Discussions

After a systematic analysis of their structural characteristics and properties, several key conclusions have emerged that may serve as valuable guidance for future research in the field, the details are discussed below:

(1) Effect of band gap: from a statistical perspective, the E_g of the multi-component chalcogenidometalates discussed in this review can be categorized into three distinct ranges: <1.5 eV, 1.5–2.5 eV, and >2.5 eV. As illustrated in Fig. 17, the photocurrent density values within the 1.5–2.5 eV range are notably higher than those in the other two ranges. This trend clearly indicates that, in most cases, multi-component chalcogenidometalates with narrower E_g values exhibit larger photocurrent densities. This can be attributed to the fact that compounds with smaller E_g have a broader spectral absorption range, enabling them to absorb photons at lower energies. Moreover, these materials are more effective at minimizing carrier recombination, which further enhances their ability to efficiently capture photons and generate a higher number of photo-generated carriers.

Fig. 17 A comparison of the banggap (E_g/eV) and photocurrent density (μA cm⁻²) of the multi-component chalcogenidometalates presented in Table 1.

(2) Impact of space groups: statistical analysis of Table 1 reveals that materials with high symmetry, such as tetragonal and orthorhombic crystal systems, generally exhibit higher photocurrents compared to those with lower symmetry, like triclinic or monoclinic crystal systems. This can be primarily attributed to the fact that high-symmetry space groups tend to have a regular electron cloud distribution and strong absorption of photons at specific wavelengths, which facilitates the generation of more carriers and enhances the photocurrent response. Furthermore, structures with higher crystalline symmetry typically exhibit stronger electron internally scattering rates, which contribute to higher charge mobility.⁶³ Notably, the cubic crystal system, despite having the highest symmetry, shows a relatively low photocurrent. This can be attributed to the absence of an intrinsic electric field and a directional separation mechanism, both of which are crucial for effectively separating the photogenerated h⁺/e⁻ and suppressing charge carrier recombination.⁶⁴ This issue can be addressed through heterojunctions or surface modifications. Therefore, an appropriately symmetrical crystal system can significantly enhance the photocurrent response. Of course, slight differences in the statistical data may stem from the influence of complex factors related to the chalcogenides and deviations caused by the limited sample size.

(3) Effect of elements: compared to group 15 metals, group 14 metal chalcogenides tend to exhibit stronger photocurrent responses. This behavior can be attributed to the periodic trends in atomic radius and electronegativity. As the atomic radius decreases within the same period and electronegativity weakens, the ease of electron escape increases, resulting in a more significant movement of electrons into the external circuit and consequently, larger photocurrents. Chalcogenide elements play a crucial role in the photoelectric properties, as demonstrated by the significantly higher photocurrent densities observed in several selenium-based multi-component chalcogenidometalates, such as Rb₂MnSnSe₄ (80 μA cm⁻²), [H₃dien][Ag₅Sn₄Se₁₂]·3H₂O (109 μA cm⁻²), and Cs₂CdGeSe₄ (180 μA cm⁻²). Therefore, it is reasonable to hypothesize that tellurium-based multi-component chalcogenidometalates may exhibit even superior photocurrent performance.

(4) Effect of polarization effects: non-centrosymmetric Hg-based chalcogenides demonstrate relatively stronger photocurrent responses, which are not only due to their polar structures but also because of the large polarization effects arising from the Jahn–Teller distortion of Hg. Additionally, the presence of Hg-containing functional motifs significantly influences the band structure, further enhancing the photocurrent response. Moreover, the polar structure could also be obtained in heteranionic structures generated from diverse chemical bonds formed by different anions (O²⁻, S²⁻, Cl⁻etc.).

(5) Impact of anion dimension: the dimensionality of the anion framework appears to have a minimal effect on the photocurrent response. Similarly, complex cations that act as charge- and space-compensating ions do not exhibit a pronounced impact. However, it is noteworthy that compounds with 3D anion structures tend to exhibit superior photocurrent densities. This is due to the more efficient charge transfer within the 3D extended network, as compared to 2D or 0D anions, which may hinder charge mobility.

6 Conclusions and prospects

In conclusion, this review comprehensively summarized the photocurrent response performances of novel chalcogenidometalates synthesized and reported thus far and offer several key conclusions have emerged that may serve as valuable guidance for future research in the field. It is important to highlight that the 67 compounds reviewed here were specifically multi-component metal chalcogenides for which photocurrent response experiments have been conducted. Although a diverse range of novel structural chalcogenides has been synthesized and studied, there remains a significant gap in photocurrent response data for many of these materials. To further accelerate the development of solar energy conversion materials based on chalcogenidometalates, it is crucial to expand the experimental database, not only for newly synthesized materials but also for previously reported multi-component metal chalcogenides. This data is essential for both performance evaluation and theoretical modeling. Moreover, the introduction of new elements or advanced doping strategies into the anionic frameworks of chalcogenidometalates could have synergistic effects on the crystal and electronic structures, enabling the tuning of band gaps and enhancing photocurrent responses. Finally, the discovery of novel chalcogenidometalates with improved photocurrent properties will benefit from rational design of their components and structures, with increased application of theoretical calculations to predict and optimize performance. We hope that this review offers a comprehensive perspective on the photocurrent response properties of multi-component chalcogenidometalates and stimulates further research into the design and development of high-performance solar energy conversion materials.

Author contributions

Chang Liu: supervision, conceptualization, writing – review & editing. Wenjing Tian: investigation, writing – original draft. Mao-Yin Ran: formal analysis, visualization. Pan Gao: formal analysis, writing – review & editing. Panpan Jing: visualization. Yi Liu: writing – review & editing. Hua Lin: conceptualization, writing – review & editing.

Data availability

No primary research results, software or code have been included and no new data were generated or analysed as part of this review.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grants No. 52202142, 52171277, and 22175175), the Science and Technology Serving Enterprise Project in University and Colleges of Xi'an Science and Technology Bureau (Grant No. 24GXFW0002), the Doctoral Scientific Research Startup Foundation of Shaanxi University of Science and Technology (2018BJ-07) and Fujian Science & Technology Innovation Laboratory for Optoelectronic Information of China (2021ZR118).

References

1. (a) I. Chung and M. G. Kanatzidis, Metal Chalcogenides: A Rich Source of Nonlinear Optical Materials, Chem. Mater., 2013, 26, 849–869; (b) F. Liang, L. Kang, Z. Lin, Y. Wu and C. Chen, Analysis and prediction of mid-IR nonlinear optical metal sulfides with diamond-like structures, Coord. Chem. Rev., 2017, 333, 57–70; (c) H. Chen, M. Y. Ran, W. B. Wei, X. T. Wu, H. Lin and Q. L. Zhu, A comprehensive review on metal chalcogenides with three-dimensional frameworks for infrared nonlinear optical applications, Coord. Chem. Rev., 2022, 470, 214706; (d) H.-D. Yang, M.-Y. Ran, W.-B. Wei, X.-T. Wu, H. Lin and Q.-L. Zhu, Recent advances in IR nonlinear optical chalcogenides with well-balanced comprehensive performance, Mater. Today Phys., 2023, 35, 101127; (e) J.-X. Zhang, P. Feng, M.-Y. Ran, X.-T. Wu, H. Lin and Q.-L. Zhu, Ga-based IR nonlinear optical materials: synthesis, structures, and properties, Coord. Chem. Rev., 2024, 502, 215617; (f) X. Liu, Y.-C. Yang, M.-Y. Li, L. Chen and L.-M. Wu, Anisotropic structure building unit involving diverse chemical bonds: a new opportunity for high-performance second-order NLO materials, Chem. Soc. Rev., 2023, 52, 8699–8720; (g) J.-X. Zhang, M.-Y. Ran, X.-T. Wu, H. Lin and Q.-L. Zhu, An overview of Mg-based IR nonlinear optical materials, Inorg. Chem. Front., 2023, 10, 5244–5257; (h) W. Zhou and S.-P. Guo, Rational Design of Novel Promising Infrared Nonlinear Optical Materials: Structural Chemistry and Balanced Performances, Acc. Chem. Res., 2024, 57, 648–660.
2. (a) H. Lin, H. Chen, J.-N. Shen, L. Chen and L.-M. Wu, Chemical Modification and Energetically Favorable Atomic Disorder of a Layered Thermoelectric Material TmCuTe₂ Leading to High Performance, Chem. – Eur. J., 2014, 20, 15401–15408; (b) H. Lin, G.-J. Tan, J.-N. Shen, S.-Q. Hao, L.-M. Wu, N. Calta, C. Malliakas, S. Wang, C. Uher, C. Wolverton and M. G. Kanatzidis, Concerted Rattling in CsAg₅Te₃ Leading to Ultralow Thermal Conductivity and High Thermoelectric Performance, Angew. Chem., Int. Ed., 2016, 55, 11431–11436; (c) R. Woods-Robinson, Y. Han, H. Zhang, T. Ablekim, I. Khan, K. A. Persson and A. Zakutayev, Wide band gap chalcogenide semiconductors, Chem. Rev., 2020, 120, 4007–4055; (d) B. Jiang, Y. Yu, J. Cui, X. Liu, L. Xie, J. Liao, Q. Zhang, Y. Huang, S. Ning and B. Jia, High-entropy-stabilized chalcogenides with high thermoelectric performance, Science, 2021, 371, 830–834; (e) A. Giri, G. Park and U. Jeong, Layer-structured anisotropic metal chalcogenides: recent advances in synthesis, modulation, and applications, Chem. Rev., 2023, 123, 3329–3442; (f) N. H. Li, Q. Zhang, X. L. Shi, J. Jiang and Z. G. Chen, Silver Copper Chalcogenide Thermoelectrics: Advance, Controversy, and Perspective, Adv. Mater., 2024, 36, 2313246; (g) P.-F. Liu, X. Li, J. Li, J. Zhu, Z. Tong, M. Kofu, M. Nirei, J. Xu, W. Yin, F. Wang, T. Liang, L. Xie, Y. Zhang, D. J. Singh, J. Ma, H. Lin, J. Zhang, J. He and B.-T. Wang, Strong low-energy rattling modes enabled liquid-like ultralow thermal conductivity in a well-ordered solid, Natl. Sci. Rev., 2024, 11, nwae216; (h) H. Chen, M.-Y. Ran, L.-H. Li, X.-T. Wu and H. Lin, [Cs₁₄Cl][Tm₇₁Se₁₁₀]: an unusual salt-inclusion chalcogenide containing different valent Tm centers and ultralow thermal conductivity, Chin. J. Struct. Chem., 2024, 43, 100397.
3. (a) L. Malavasi and S. Margadonna, Structure–properties correlations in Fe chalcogenide superconductors, Chem. Soc. Rev., 2012, 41, 3897–3911; (b) Q. Si, R. Yu and E. Abrahams, High-temperature superconductivity in iron pnictides and chalcogenides, Nat. Rev. Mater., 2016, 1, 1–15; (c) N. Zaki, G. Gu, A. Tsvelik, C. Wu and P. D. Johnson, Time-reversal Symmetry Breaking in the Fe-chalcogenide Superconductors, Proc. Natl. Acad. Sci. U. S. A., 2021, 118, e2007241118; (d) R. M. Fernandes, A. I. Coldea, H. Ding, I. R. Fisher, P. J. Hirschfeld and G. Kotliar, Iron pnictides and chalcogenides: a new paradigm for superconductivity, Nature, 2022, 601, 35–44.
4. (a) M. Enayat, Z. Sun, U. R. Singh, R. Aluru, S. Schmaus, A. Yaresko, Y. Liu, C. Lin, V. Tsurkan and A. Loidl, Real-space imaging of the atomic-scale magnetic structure of Fe_1+yTe, Science, 2014, 345, 653–656; (b) Y.-J. Zheng, Y.-F. Shi, C.-B. Tian, H. Lin, L.-M. Wu, X.-T. Wu and Q.-L. Zhu, An Unprecedented Pentanary Chalcohalide with the Mn Atoms in Two Chemical Environments: Unique Bonding Characteristics and Magnetic Properties, Chem. Commun., 2019, 55, 79–82; (c) S. Licciardello, J. Buhot, J. Lu, J. Ayres, S. Kasahara, Y. Matsuda, T. Shibauchi and N. E. Hussey, Electrical resistivity across a nematic quantum critical point, Nature, 2019, 567, 213–217; (d) H. Liu and Y. Xue, van der Waals epitaxial growth and phase transition of layered FeSe₂ nanocrystals, Adv. Mater., 2021, 33, 2008456.
5. (a) C. Coughlan, M. Ibanez, O. Dobrozhan, A. Singh, A. Cabot and K. M. Ryan, Compound copper chalcogenide nanocrystals, Chem. Rev., 2017, 117, 5865–6109; (b) Y. Zhu, L. Wang, Y. Liu, L. Shao and X. Xia, In situ Hydrogenation Engineering of ZnIn₂S₄ for Promoted visible-light Water Splitting, Appl. Catal., B, 2019, 241, 483–490; (c) Y. Wang, B. Ren, J.-Z. Ou, K. Xu, C. Yang, Y. Li and H. Zhang, Engineering Two-dimensional Metal Oxides and Chalcogenides for Enhanced Electro- and Photocatalysis, Sci. Bull., 2021, 66, 1228–1252; (d) L. Wu, Y. Li, G.-Q. Liu and S.-H. Yu, Polytypic metal chalcogenide nanocrystals, Chem. Soc. Rev., 2024, 53, 9832–9873.
6. (a) Y.-J. Gao, H.-Y. Sun, J.-L. Li, X.-H. Qi, K.-Z. Du, Y.-Y. Liao, X.-Y. Huang, M.-L. Feng and M. G. Kanatzidis, Selective Capture of Ba²⁺, Ni²⁺, and Co²⁺ by a Robust Layered Metal Sulfide, Chem. Mater., 2020, 32, 1957–1963; (b) W.-A. Li, J.-R. Li, B. Zhang, H.-Y. Sun, J.-C. Jin, X.-Y. Huang and M.-L. Feng, Layered Thiostannates with Distinct Arrangements of Mixed Cations for the Selective Capture of Cs⁺, Sr²⁺, and Eu³⁺ Ions, ACS Appl. Mater. Interfaces, 2021, 13, 10191–10201; (c) C. Gu, H.-M. Xu, S.-K. Han, M.-R. Gao and S.-H. Yu, Soft chemistry of metastable metal chalcogenide nanomaterials, Chem. Soc. Rev., 2021, 50, 6671–6683; (d) K. Saito, M. Morita, T. Okada and M. Ogawa, Designed functions of oxide/hydroxide nanosheets via elemental replacement/doping, Chem. Soc. Rev., 2024, 53, 10523–10574.
7. (a) S.-L. Ju, W. Bai, L.-M. Wu, H. Lin, C. Xiao, S.-T. Cui, Z. Li, S. Kong, Y. Liu, D.-Y. Liu, G.-B. Zhang, Z. Sun and Y. Xie, Evidence for Itinerant Carriers in Anisotropic Narrow-gap Semiconductor by Angle-Resolved Photoemission Spectroscopy, Adv. Mater., 2018, 30, 1704733; (b) R. Woods-Robinson, Y. Han, H. Zhang, T. Ablekim, I. Khan, K. A. Persson and A. Zakutayev, Wide Band Gap Chalcogenide Semiconductors, Chem. Rev., 2020, 120, 4007–4055; (c) Y. Wang, S. R. Kavanagh, I. Burgués-Ceballos, A. Walsh, D. O. Scanlon and G. Konstantatos, Cation Disorder Engineering Yields AgBiS₂ Nanocrystals with Enhanced Optical Absorption for Efficient Ultrathin Solar Cells, Nat. Photonics, 2022, 16, 235–241; (d) H. Yang, Z. Ma and Q. Wang, Shortwave-Infrared Silver Chalcogenide Quantum Dots for Optoelectronic Devices, ACS Nano, 2024, 18, 30123–30131; (e) W. Jiang, S. Wu, D. Xu, L. Tu, Y. Xie, P. Pasqués-Gramage, P. G. Boj, M. A. Díaz-García, F. Li and J. Wu, Stable Xanthene Radicals and Their Heavy Chalcogen Analogues Showing Tunable Doublet Emission from Green to Near-infrared, Angew. Chem., Int. Ed., 2025, 138, e202418762.
8. D. Paul and D. Devaprakasam, A Novel Approach to Enhance Performance, Stability and Longevity of the Solar Cells by Mitigating UV-induced Degradation with Monolayer-Boosted Nano-TiO₂ Coatings, Sol. Energy, 2025, 285, 113118.
9. K. Hashimoto, H. Irie and A. Fujishima, TiO₂ Photocatalysis: A Historical Overview and Future Prospects, Jpn. J. Appl. Phys., 2005, 44, 8269.
10. H. P. Maruska and A. K. Ghosh, Photocatalytic Decomposition of Water at Semiconductor Electrodes, Sol. Energy, 1978, 20, 443–458.
11. K. van Benthem, C. Elsässer and R. French, Bulk Electronic Structure of SrTiO₃: Experiment and Theory, J. Appl. Phys., 2001, 90, 6156–6164.
12. X. Y. Song, W. Q. Li, D. He, H. G. Wu, Z. J. Ke, C. Z. Jiang, G. M. Wang and X. H. Xiao, The “Midas Touch” transformation of TiO₂ nanowire arrays during visible light photoelectrochemical performance by carbon/nitrogen coimplantation, Adv. Energy Mater., 2018, 8, 1800165.
13. A. Paliwal, K. P. S. Zanoni, C. Roldán-Carmona, N. Rodkey and H. J. Bolink, Vacuum-Deposited Bifacial Perovskite Solar Cells, ACS Energy Lett., 2024, 9, 4587–4595.
14. C. S. Ferekides, U. Balasubramanian, R. Mamazza, V. Viswanathan, H. Zhao and D. L. Morel, CdTe thin film solar cells: device and technology issues, Sol. Energy, 2004, 77, 823–830.
15. T. Zhang, Y. Yang, D. Liu, S. C. Tse, W. Cao, Z. Feng, S. Chen and L. Qian, High efficiency solution-processed thin-film Cu(In,Ga)(Se,S)2 solar cells, Energy Environ. Sci., 2016, 9, 3674–3681.
16. L.-P. Yu and A. Zunger, Identification of Potential Photovoltaic Absorbers Based on First-Principles Spectroscopic Screening of Materials, Phys. Rev. Lett., 2012, 108, 068701.
17. M.-S. Hybertsen and S.-G. Louie, First-principles Theory of Quasiparticles: Calculation of Band Gaps in Semiconductors and Insulators, Phys. Rev. Lett., 1985, 55, 1418–1421.
18. H.-Y. Luo, J. Zhou and S. Cao, The Rare Examples of Chalcogenogermanates Combined with Trivalent Vanadium Complexes, Dalton Trans., 2019, 48, 10907–10914.
19. S. Cao, Y. Chen, X. Liu, J. Zhou and J. Liu, The First Selenidostannate Directed by Low-Valent Vanadium(II) Complex: Photocurrent Response and Magnetic Properties, Inorg. Chem. Commun., 2021, 133, 108862.
20. X. Tian, G. Teri, M. Shele, E. Namila, L. Qi, M. Liu and M.-H. Baiyin, Five New TM-Sn-Q (TM = Transition Metals; Q = S, Se) Photoelectrocatalytic Materials, Polyhedron, 2022, 217, 115729.
21. M. Shele, X. Tian and M. Baiyin, Solvothermal Synthesis and Properties of Three Antimony Chalcogenides Containing Transition Metal Zinc, J. Solid State Chem., 2021, 302, 122401.
22. L. Zhang, H. Zhao, X. Liu, G. Teri and M. Baiyin, Syntheses, Crystal Structure, and Photoelectric Properties of Two Zn-Based Chalcogenidoantimonates Zn–Sb–Q (Q = S, Se), Phys. Chem. Chem. Phys., 2023, 25, 29709–29717.
23. L. Zhang, N. Li, G. Teri, M. Shele, E. Namila, S. Bai and M. Baiyin, Syntheses, Crystal Structure and Properties of Two Chalcogenidoantimonates Mn(En)₃Sb₂S₄ and Co(En)₃Sb₂Se₄, Polyhedron, 2023, 241, 116470.
24. J. Tang, X. Wang, P. Sun, J. Wu, J. Li, Z. Wang and T. Wu, The First Observation That Metal Chalcogenide Supertetrahedral Cluster Is Corner-Coordinated by Neutral Amine Group, J. Solid State Chem., 2022, 308, 122935.
25. X. Huang, S.-H. Yang, W. Liu and S.-P. Guo, Ba₃HgGa₂S₇: A Zero-Dimensional Quaternary Sulfide Featuring a Unique [Hg₂Ga₄S₁₄]¹²⁻ String and Exhibiting a High Photocurrent Response, Inorg. Chem., 2022, 61, 12954–12958.
26. Y. Liu, Y. Li, J. Zhao, R. Zhang, M. Ji, Z. You and Y. An, Solvothermal Syntheses, Characterizations and Semiconducting Properties of Four Quaternary Thioargentates Ba₂AgInS₄, Ba₃Ag₂Sn₂S₈, BaAg₂MS₄ (M = Sn, Ge), J. Alloys Compd., 2020, 815, 152413.
27. Y. Tian, J. Zhang, W. Wang and D. Jia, Ternary 3D Framework [Ag₅Sn₄Se₁₂]³⁻: Solvothermal Synthesis, Crystal Structure and Photoelectric Properties of an Organic Silver-Rich Selenidostannate Hybrid, Inorg. Chem. Commun., 2021, 131, 108799.
28. Y. Zhang, D. Hu, H. Yang, J. Lin and T. Wu, Synthesis, Crystal Structure, near-IR Photoelectric Response of Two 1-D Selenides: [Cu₂MSe₅]·[Mn(H⁺-En)2(En)] (M = Ge, Sn), J. Solid State Chem., 2017, 251, 61–64.
29. K.-Z. Du, X.-H. Qi, M.-L. Feng, J.-R. Li, X.-Z. Wang, C.-F. Du, G.-D. Zou, M. Wang and X.-Y. Huang, Synthesis, Structure, Band Gap, and Near-Infrared Photosensitivity of a New Chalcogenide Crystal, (NH₄)₄Ag₁₂Sn₇Se₂₂, Inorg. Chem., 2016, 55, 5110–5112.
30. C. Cui, H. Pan, L. Wang and M.-H. Baiyin, Transition Metal Germanium Chalcogenide Materials: Solvothermal Syntheses, Flexible Crystal, Structures, and Photoelectric Response Property, Cryst. Growth Des., 2024, 24, 1227–1234.
31. Y. Li, X. Song, Y. Liu, Y. Guo, Y. Sun, M. Ji, Z. You and Y. An, Syntheses, Structures, and Photocatalytic Properties of Open-Framework Ag-Sn-S Compounds, Dalton Trans., 2020, 49, 11708–11714.
32. G. Teri, X. Liu, N. Li, M. Shele, E. Namila, L. Qi, S. Bai and M. Baiyin, Strong Photoelectric Properties of Mnerties of Open-Framework Ag-Sn-S Compounds Crystal, (NHRich Selenidostann, Eur. J. Inorg. Chem., 2023, 26, e202200607.
33. G. Teri, N. Li, S. Bai, E. Namila and M.-H. Baiyin, Synthesis, Crystal Structure, Photocatalysis, Photocurrent Response: One-Dimensional K₂HgSnSe₄ and Three-Dimensional Na₆Cu₈Sn₃Se₁₃, CrystEngComm, 2021, 23, 6079–6085.
34. Y. Li, X. Song, Y. Zhong, Y. Guo, M. Ji, Z. You and Y. An, Temperature Controlling Valance Changes of Crystalline Thioarsenates and Thioantimonates, J. Alloys Compd., 2021, 872, 159591.
35. C. Liu, H.-D. Yang, P.-P. Hou, Y. Xiao, Y. Liu and H. Lin, Cs₃CuAs₄Q₈(Q = S, Se): Unique Two-Dimensional Layered Inorganic Thioarsenates with the Lowest Cu-to-As Ratio and Remarkable Photocurrent Responses, Dalton Trans., 2022, 51, 904–909.
36. C. Zhang, S.-H. Zhou, Y. Xiao, H. Lin and Y. Liu, Interesting Dimensional Transition through Changing Cations as the Trigger in Multinary Thioarsenates Displaying Variable Photocurrent Response and Optical Anisotropy, Inorg. Chem. Front., 2022, 9, 5820–5827.
37. X. Chen, S.-H. Zhou, C. Zhang, H. Lin and Y. Liu, A Novel Bifunctional Thioarsenate Based on Unprecedented Molecular [Cd₄As₈Se₁₆(Se₂)₂]⁸⁻ Cluster Anions, Chem. Commun., 2023, 59, 12124–12127.
38. J. Tang, F. Liang, W. Xing, C. Tang, W. Yin, B. Kang and J. Deng, AgMAsS₃ (M = Cd, Hg): Double d10 Cation-Containing Thioarsenites(III) Exhibiting High Photocurrent Response and Moderate Second Harmonic Generation, Inorg. Chem., 2023, 62, 14739–14747.
39. H. Wang, J.-M. Yu, N. Wang, L.-L. Xiao, J.-P. Yu, Q. Xu, B. Zheng, F.-F. Cheng and W.-W. Xiong, Two Silver Chalcogenidoantimonates Synthesized in Piperazine and Their High Performances for Visible-Light Driven Cr(VI) Reduction, J. Solid State Chem., 2021, 300, 122276.
40. N. Li, L. Zhang, J. Chen, G. Teri, M. Shele, E. Namila, S. Bai and M. Baiyin, Two New Gallium(III)-Thioantimonates TM(Tren)GaSbS₄ (TM = Mn, Fe): Syntheses, Crystal Structure and Properties, Inorg. Chem. Commun., 2022, 146, 110214.
41. L. Zhang, F. Qi, M. Shele, E. Namila, L. Qi and M.-H. Baiyin, Solvothermal Synthesis and Characterization of One-Dimensional [Mn(En)₃]CdSb₂Se₅, J. Chem. Crystallogr., 2023, 53, 145–151.
42. Y. Xiao, M.-M. Chen, Y.-Y. Shen, P.-F. Liu, H. Lin and Y. Liu, A₃Mn₂Sb₃S₈ (A = K and Rb): A New Type of Multifunctional Infrared Nonlinear Optical Material Based on Unique Three-Dimensional Open Frameworks, Inorg. Chem. Front., 2021, 8, 2835–2843.
43. C. Liu, P. Hou, W. Chai, J. Tian, X. Zheng, Y. Shen, M. Zhi, C. Zhou and Y. Liu, Hydrazine-Hydrothermal Syntheses, Characterizations and Photoelectrochemical Properties of Two Quaternary Chalcogenidoantimonates(III): BaCuSbQ₃ (Q = S, Se), J. Alloys Compd., 2016, 679, 420–425.
44. Y. Xiao, S.-H. Zhou, R. Yu, Y. Shen, Z. Ma, H. Lin and Y. Liu, Rb₂CuSb₇S₁₂: Quaternary Antimony-Rich Semiconductor Featuring a Three-Dimensional Open Framework and Exhibiting an Intriguing Photocurrent Response, Inorg. Chem., 2021, 60, 9263–9267.
45. R. Wang, X. Zhang, J. He, C. Zheng, J. Lin and F. Huang, Synthesis, Crystal Structure, Electronic Structure, and Photoelectric Response Properties of KCu₂SbS₃, Dalton Trans., 2016, 45, 3473–3479.
46. X. Zhang, J. He, R. Wang, K. Bu, J. Li, C. Zheng, J. Lin and F. Huang, Enhancement of Solar Energy Absorption and Optoelectronic Properties of SrCuSbS₃ by Lead Doping, Sol. RRL, 2018, 2, 1800021.
47. Y. Liu, L. Geng, Z. Xue, Z. Song, D. Xuan, S. Song and Z. Zhao, Syntheses, Crystal Structures, Photocatalysis, and Photoelectric Responses of Quaternary Sulfides ACuZnS₂ (A = K, Rb, Cs), Inorg. Chem. Commun., 2022, 146, 110108.
48. Y. Liu, X. Song, Y. Guo, Y. Zhong, Y. Li, Y. Sun, M. Ji, Z. You and Y. An, Mild Solvothermal Syntheses and Characterizations of Two Layered Sulfides Ba₂Cu₂Cd₂S₅ and Ba₃Cu₄Hg₄S₉, J. Alloys Compd., 2020, 829, 154586.
49. M. Y. Li, X. Y. Xie, X. T. Wu, X. F. Li and H. Lin, Quaternary Selenophosphate Cs₂ZnP₂Se₆ Featuring Unique One-dimensional Chains and Exhibiting Remarkable Photo-electrochemical Response, Chin. J. Struct. Chem., 2021, 40, 246–255.
50. H. Lin, J. N. Shen, W. W. Zhu, Y. Liu, X. T. Wu, Q. L. Zhu and L. M. Wu, Two new phases in the ternary RE–Ga–S systems with unique interlinkage of GaS₄ building units: synthesis, structure, and properties, Dalton Trans., 2017, 46, 13731–13738.
51. Y. F. Shi, X. F. Li, Y. X. Zhang, H. Lin, Z. J. Ma, L. M. Wu, X. T. Wu and Q. L. Zhu, [(Ba₁₉Cl₄)(Ga₆Si₁₂O₄₂S₈)]: a Two-Dimensional Wide-Band-Gap Layered Oxysulfide with Mixed-Anion Chemical Bonding and Photocurrent Response, Inorg. Chem., 2019, 58, 6588–6592.
52. W.-F. Zhou, W.-D. Yao, R.-L. Tang, G. Xue and S.-P. Guo, Second-order Nonlinear Optical and Photoelectric Properties of Zn₄B₆O₁₂S, J. Alloys Compd., 2021, 867, 158879.
53. S. Al Bacha, S. Saitzek, P. Roussel, M. Huvé, E. E. McCabe and H. Kabbour, Low Carrier Effective Masses in Photoactive Sr₂Sb₂O₂Q₃ (Q = S, Se): The Role of the Lone Pair, Chem. Mater., 2023, 35, 9528–9541.
54. S. Al Bacha, S. Saitzek, E. E. McCabe and H. Kabbour, Photocatalytic and Photocurrent Responses to Visible Light of the Lone-Pair-Based Oxysulfide Sr₆Cd₂Sb₆S₁₀O₇, Inorg. Chem., 2022, 61, 18611–18621.
55. D. Wong, P. Lee, S. Gao, X. Wang, H. Y. Qi and F. S. Kit, The photoelectric effect: experimental confirmation concerning a widespread misconception in the theory, Eur. J. Phys., 2011, 32, 1059.
56. J. Cen, Q. Wu, M. Liu and A. Orlov, Developing new understanding of photoelectrochemical water splitting via in-situ techniques: A review on recent progress, Green Energy Environ., 2017, 2, 100–111.
57. W. Zhang, J. Ma, L. Xiong, H.-Y. Jiang and J. Tang, Well-Crystallized α-FeOOH Cocatalysts Modified BiVO₄ Photoanodes for Efficient and Stable Photoelectrochemical Water Splitting, ACS Appl. Energy Mater., 2020, 3, 5927–5936.
58. (a) Y.-Y. Li, B.-X. Li, G. Zhang, L.-J. Zhou, H. Lin, J.-N. Shen, C.-Y. Zhang, L. Chen and L.-M. Wu, Syntheses, Characterization, and Optical Properties of Centrosymmetric Ba₃(BS₃)_1.5(MS₃)_0.5 and Noncentrosymmetric Ba₃(BQ₃)(SbQ₃), Inorg. Chem., 2015, 54, 4761–4767; (b) H. Lin, Y. Y. Li, M. Y. Li, Z. J. Ma, L. M. Wu, X. T. Wu and Q. L. Zhu, Centric-to-acentric structure transformation induced by a stereochemically active lone pair: a new insight for design of IR nonlinear optical materials, J. Mater. Chem. C, 2019, 7, 4638–4643; (c) C. Liu, Y. Xiao, H. Wang, W. Chai, X. Liu, D. Yan, H. Lin and Y. Liu, One-Dimensional Chains in Pentanary Chalcogenides A₂Ba₃Cu₂Sb₂S₁₀ (A = K, Rb, Cs) Displaying a Photocurrent Response, Inorg. Chem., 2020, 59, 1577–1581; (d) M. Yan, H.-G. Xue and S.-P. Guo, Recent Achievements in Lone-Pair Cation-Based Infrared Second-Order Nonlinear Optical Materials, Cryst. Growth Des., 2021, 21, 698–720; (e) C. Liu, S.-H. Zhou, Y. Xiao, C. Zhang, H. Lin and Y. Liu, Aliovalent-cation-substitution-induced structure transformation: a new path toward high-performance IR nonlinear optical materials, J. Mater. Chem. C, 2021, 9, 15407–15414; (f) M.-M. Chen, Z. Ma, B.-X. Li, W.-B. Wei, X.-T. Wu, H. Lin and Q.-L. Zhu, M₂As₂Q₅ (M = Ba, Pb; Q = S, Se): A source of infrared nonlinear optical materials with excellent overall performance activated by multiple discrete arsenate anions, J. Mater. Chem. C, 2021, 9, 1156–1163; (g) Y. Xiao, M. M. Chen, Y. Y. Shen, P. F. Liu, H. Lin and Y. Liu, A₃Mn₂Sb₃S₈ (A = K, Rb): A new type of multifunctional infrared nonlinear optical materials based on unique three-dimensional open frameworks, Inorg. Chem. Front., 2021, 8, 2835–2843; (h) H.-J. Zhao, H.-D. Yang, P.-F. Liu and H. Lin, From Cc to P6₃mc: Structural Variation in La₃S₂Cl₂[SbS₃] and La₃OSCl₂[SbS₃] Induced by the Isovalent Anion Substitution, Cryst. Growth Des., 2022, 22, 1437–1444; (i) F. Xu, X. Xu, B. Li, G. Zhang, C. Zheng, J. Chen and N. Ye, Hg₃AsS₄X (X = Cl and Br): two Hg-based chalcogenides as long-wave infrared nonlinear optical crystals with superior comprehensive performances, Inorg. Chem. Front., 2024, 11, 2105–2115; (j) Y. Zhou, L.-T. Jiang, X.-M. Jiang, B.-W. Liu and G.-C. Guo, Mixed-anion square-pyramid [SbS₃I₂] units causing strong second-harmonic generation intensity and large birefringence, Chin. Chem. Lett., 2024, 35, 109740.
59. (a) M. Y. Li, Z. J. Ma, B. X. Li, X. T. Wu, H. Lin and Q. L. Zhu, HgCuPS₄: An Exceptional Infrared Nonlinear Optical Material with Defect Diamond-like Structure, Chem. Mater., 2020, 32, 4331–4339; (b) Y. Chu, P. Wang, H. Zeng, S. Cheng, X. Su, Z. Yang, J. Li and S. Pan, Hg₃P₂S₈: A New Promising Infrared Nonlinear Optical Material with a Large Second-Harmonic Generation and a High Laser-Induced Damage Threshold, Chem. Mater., 2021, 33, 6514–6521; (c) Y. Chu, H. Wang, T. Abutukadi, Z. Li, M. Mutailipu, X. Su, Z. Yang, J. Li and S. Pan, Zn₂HgP₂S₈: A Wide Bandgap Hg-Based Infrared Nonlinear Optical Material with Large Second-Harmonic Generation Response, Small, 2023, 19, 2305074; (d) Y. Chu, H. Wang, Q. Chen, X. Su, Z. Chen, Z. Yang, J. Li and S. Pan, “Three-in-One”: A New Hg-Based Selenide Hg₇P₂Se₁₂ Exhibiting Wide Infrared Transparency Range and Strong Nonlinear Optical Effect, Adv. Funct. Mater., 2024, 34, 2314933; (e) A.-Y. Wang, S.-H. Zhou, M.-Y. Ran, X.-T. Wu, H. Lin and Q.-L. Zhu, Regulating the Key Performance Parameters for Hg-based IR NLO Chalcogenides via Bandgap Engineering Strategy, Chin. Chem. Lett., 2024, 35, 109377; (f) M.-Y. Ran, S.-H. Zhou, W.-B. Wei, B.-X. Li, X.-T. Wu, H. Lin and Q.-L. Zhu, Breaking through the Trade-Off between Wide Band Gap and Large SHG Coefficient in Mercury-based Chalcogenides for IR Nonlinear Optical Application, Small, 2024, 20, 2304563.
60. (a) S.-P. Guo, Y. Chi and G.-C. Guo, Recent Achievements on Middle and Far-Infrared Second-Order Nonlinear Optical Materials, Coord. Chem. Rev., 2017, 335, 44–57; (b) M.-M. Chen, H.-G. Xue and S.-P. Guo, Multinary Metal Chalcogenides with Tetrahedral Structures for Second-Order Nonlinear Optical, Photocatalytic, and Photovoltaic Applications, Coord. Chem. Rev., 2018, 368, 115–133; H. Chen, W.-B. Wei, H. Lin and X.-T. Wu, Transition-metal-based chalcogenides: A rich source of infrared nonlinear optical materials, Coord. Chem. Rev., 2021, 448, 214154; (c) Y. K. Kang, H. Lee, T. D. C. Ha, J. K. Won, H. Jo, K. M. Ok, S. Ahn, B. Kang, K. Ahn, Y. Oh and M.-G. Kim, Thiostannate Coordination Transformation-Induced Self-Crosslinking Chalcogenide Aerogel with Local Coordination Control and Effective Cs⁺ Remediation Functionality, J. Mater. Chem. A, 2020, 8, 3468–3480; (d) P. Feng, J.-X. Zhang, M.-Y. Ran, X.-T. Wu, H. Lin and Q. L. Zhu, Rare-earth-based chalcogenides and their derivatives: an encouraging IR nonlinear optical material candidate, Chem. Sci., 2024, 15, 5869–5896.
61. (a) R. Wang, F. Liang, F. Wang, Y. Guo, X. Zhang, Y. Xiao, K. Bu, Z. Lin, J. Yao, T. Zhai and F. Q. Huang, Sr₆Cd₂Sb₆O₇S₁₀: Strong SHG Response Activated by Highly Polarizable Sb/O/S Groups, Angew. Chem., Int. Ed., 2019, 58, 8078–8081; (b) Y.-F. Shi, W.-B. Wei, X.-T. Wu, H. Lin and Q.-L. Zhu, Recent progress in oxychalcogenides as IR nonlinear optical materials, Dalton Trans., 2021, 50, 4112–4118; (c) H. Yan, Y. Matsushita, K. Yamaura and Y. Tsujimoto, La₃Ga₃Ge₂S₃O₁₀: An Ultraviolet Nonlinear Optical Oxysulfide Designed by Anion-Directed Band Gap Engineering, Angew. Chem., Int. Ed., 2021, 60, 26561–26565; (d) Y. Zhang, H. Wu, Z. Hu and H. Yu, Oxychalcogenides: A Promising Class of Materials for Nonlinear Optical Crystals with Mixed-Anion Groups, Chem. – Eur. J., 2022, 29, e202203597; (e) M.-Y. Ran, S.-H. Zhou, B.-X. Li, W.-B. Wei, X.-T. Wu, H. Lin and Q.-L. Zhu, Enhanced Second-Harmonic-Generation Efficiency and Birefringence in Melillite Oxychalcogenides Sr₂MGe₂OS₆ (M = Mn, Zn, and Cd), Chem. Mater., 2022, 34, 3853–3861; (f) R. Wang, F. Liang, X. Liu, Y. Xiao, Q. Liu, X. Zhang, L.-M. Wu, L. Chen and F. Huang, Heteroanionic Melilite Oxysulfide: A Promising Infrared Nonlinear Optical Candidate with a Strong Second-Harmonic Generation Response, Sufficient Birefringence, and Wide Bandgap, ACS Appl. Mater. Interfaces, 2022, 14, 23645–23652; (g) Y.-F. Shi, Z. Ma, B.-X. Li, X.-T. Wu, H. Lin and Q.-L. Zhu, Phase matching achieved by isomorphous substitution in IR nonlinear optical material Ba₂SnSSi₂O₇ with an undiscovered [SnO₄S] functional motif, Mater. Chem. Front., 2022, 6, 3054–3061; (h) M.-Y. Ran, S.-H. Zhou, W.-B. Wei, B.-X. Li, X.-T. Wu, H. Lin and Q.-L. Zhu, Rational Design of a Rare-Earth Oxychalcogenide Nd₃[Ga₃O₃S₃][Ge₂O₇] with Superior Infrared Nonlinear Optical Performance, Small, 2023, 19, 2300248; (i) M.-Y. Ran, S.-H. Zhou, X.-T. Wu, H. Lin and Q.-L. Zhu, The first Hg-based oxychalcogenide Sr₂HgGe₂OS₆: achieving balanced IR nonlinear optical properties through synergistic cation and anion substitution, Mater. Today Phys., 2024, 44, 101442; (j) M.-Y. Ran, S.-H. Zhou, B.-X. Li, X.-T. Wu, H. Lin and Q.-L. Zhu, Balanced IR Nonlinear Optical Performance Achieved by Cation–Anion Module Co-Substitution in V-Based Salt-Inclusion Oxychalcogenides, Chem. Mater., 2024, 36, 11996–12005.
62. (a) H. Lin, W.-B. Wei, H. Chen, X.-T. Wu and Q.-L. Zhu, Rational design of infrared nonlinear optical chalcogenides by chemical substitution, Coord. Chem. Rev., 2020, 406, 213150; (b) G. Zou and K. M. Ok, Novel ultraviolet (UV) nonlinear optical (NLO) materials discovered by chemical substitution-oriented design, Chem. Sci., 2020, 11, 5404–5409; (c) M.-Y. Ran, A. Y. Wang, W.-B. Wei, X.-T. Wu, H. Lin and Q.-L. Zhu, Recent progress in the design of IR nonlinear optical materials by partial chemical substitution: Structural evolution and performance optimization, Coord. Chem. Rev., 2023, 481, 215059.
63. (a) Y. Z. Pei, X. Y. Shi, A. LaLonde, H. Wang, L. D. Chen and G. J. Snyder, Convergence of electronic bands for high performance bulk thermoelectrics, Nature, 2011, 473, 66–69; (b) Y. Y. Li, Y. Diao, X. Y. Wang, X. F. Tian, Y. Hu, B. Zhang and D. F. Yang, Zn₄B₆O₁₃: Efficient Borate Photocatalyst with Fast Carrier Separation for Photodegradation of Tetracycline, Inorg. Chem., 2020, 59, 13136–13143.
64. (a) Z. L. Li, Z. Q. Li, C. L. Zuo and X. S. Fang, Application of Nanostructured TiO₂ in UV Photodetectors: A Review, Adv. Mater., 2022, 34, 2109083; (b) H. T. Huang, J. Wang, Y. Liu, M. Y. Zhao, N. S. Zhang, Y. F. Hu, F. T. Fan, J. Y. Feng, Z. S. Li and Z. G. Zou, Stacking textured films on lattice-mismatched transparent conducting oxides via matched Voronoi cell of oxygen sublattice, Nat. Mater., 2024, 23, 383–390.

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