Catalyst-assisted growth of CsPbBr₃ perovskite nanowires

Abstract

Halide perovskites (HPs), particularly at the nanoscale, attract attention due to their unique optical properties compared to other semiconductors. They exhibit bright emission, defect tolerance, and a broad tunable band gap. The ability to directly transport charge carriers along the HPs nanowires (NWs) has led to the development of methods for their synthesis. Most of these methods involve some version of an oriented attachment step with various modifications. In this study, we introduce CsPbBr₃ nanowires produced via the solution–solid–solid (SSS) catalyst-assisted growth mechanism for the first time. We explored the kinetics of this process and examined the connection between the catalyst phase and its reactivity. We show how HP NWs grow with different SSS catalysts (i.e., Ag₂S, Ag₂Se, CuS) and discuss the required conditions for successful synthesis utilizing this mechanism. This method opens up a new avenue for producing HP NWs, which can be used to design and form new types of hybrid nanostructures.

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Introduction

Halide perovskites (HPs) have been valued for their unique characteristics in various fields such as photovoltaics,^1,2 optoelectronics,^3,4 and catalysis.^5,6 Lately, the study of quantum-confined colloidal HP nanocrystals has emerged as a significant area of research due to their defect tolerance,⁷ wide band gap tunability,^8,9 and bright emission capabilities.^9,10

As with other semiconductors, the one-dimensional (1D) morphology has been the focus of many studies and applications. New methodologies for synthesizing crystalline HP nanowires (NWs) and nanorods have been developed, driven by the prospect of excellent charge carriers transport within such nanocrystals.¹¹ For instance, Zhang et al. synthesized the first CsPbBr₃ perovskite NWs with a diameter of about 10 nm;¹² afterwards, through a stepwise purification process, they managed to reduce the diameter of these NWs to achieve strong quantum confinement at d ≈ 2 nm.¹³ Other homogeneous NWs with a tunable width were also prepared using short chain carboxylic acids and room temperature,^11,14,15 or by harnessing the oriented attachment mechanism, where CsPbX₃ (X = halide) cubes assemble to form the desired NW product.^16–18 Due to the cubic nature of these materials, they do not prefer anisotropic growth, as known for wurtzite structures. The previously reported methods are based on the oriented attachment mechanism, where CsPbX₃ cubes are attached to form 1D morphology; the synthetic tools that allow this process include low temperature, long time, and changing ligand concentration. However, the catalyst-assisted growth mechanism for growing perovskite nanowires has not yet been reported.

Herein, we describe the synthesis of CsPbBr₃ nanowires via the solution–solid–solid (SSS) mechanism for the first time. We used semiconductor nanoparticles (Ag₂S, Ag₂Se, Cu₂S) that undergo a phase transition to a superionic phase at the reaction temperature. This reactive phase is typically used as a catalyst for growing metal chalcogenides 1D nanocrystals.^19–21 We succeeded in forming CsPbBr₃ perovskite nanowires with μm length in very short synthesis times. Furthermore, we studied the formation kinetics and the effect of the catalyst's type, phase, and composition on the nanowires’ growth by real-time monitoring of phase transitions of the catalysts via in situ X-ray diffraction (XRD) in solution.

Preparing HPs using the SSS mechanism offers the benefit of catalyst-assisted growth, significantly improving synthesis time and reaction yield. The success of this approach suggests that other catalyst-assisted growth methods, such as solution–liquid–solid (SLS) and vapor–liquid–solid (VLS), could also be employed for HP formation. Notably, these methods are well-suited for large-scale nanowire synthesis, a key factor for advancing nanowire-based device manufacturing.^22,23 Additionally, the flexibility of these catalytic routes holds great potential for developing hybrid nanostructures incorporating HPs, thereby broadening the scope of potential applications.^24,25

Experimental section

Materials

All reactants and solvents were purchased from commercial sources and used as received unless indicated otherwise. Oleylamine (OAm, 98%), dodecanethiol (DDT, 98.5%), oleic acid (OA, 90%), octadecylamine (ODA, 90%), sulfur powder (S, 99.98%), and sodium diethyldithiocarbamate trihydrate (NadtcEt₂·3H₂O, ≥99.0%; abbreviated in the text as NadtcEt₂ for simplicity) were purchased from Sigma-Aldrich. Octadecene (ODE, 90%) and anhydrous toluene (99.8%) were purchased from Alfa Aesar. Anhydrous copper(II) acetate (CuAc₂, 97%), cesium carbonate (Cs₂CO₃, 99%), CdO powder (99.999%), and selenium powder (Se, 99.99%) were purchased from Strem. Lead bromide was purchased from Apollo Scientific Limited (PbBr, 99.999%). Silver nitrate (AgNO₃, 99.8%) was purchased from Fisher Scientific. The solvents n-hexane (C₆H₁₄, 95%), toluene (C₇H₈, 99.7%), 2-propanol (IPA, 99.8%), and ethanol (EtOH, absolute, 99%) were purchased from Bio-Lab Chemicals, Israel.

Synthetic procedures

[AgdtcEt₂] preparation. According to previously published procedures,²⁶ AgNO₃ and NadtcEt₂ were separately dissolved in deionized water at a 1 : 1 molar ratio. After mixing, stirring, vacuum-filtration, and washing, chloroform was used for recrystallization.

Colloidal syntheses. All the synthetic procedures described hereinafter were conducted using standard air-free Schleck-line techniques (inert N₂ atmosphere), 25 mL three-neck borosilicate round bottom flasks, and PTFE-coated magnetic stirrings bars.

OAm, ODE, and OA were mixed under vacuum at 120 °C overnight before further use.

Ag₂S nanoparticles synthesis. 25 mg of [AgdtcEt₂] was mixed with 2 mL OAm and 3 mL DDT under vacuum for 5 min at room temperature; then, the temperature was raised to 200 °C under N₂ atmosphere for 30 min before cooling down to room temperature. 5 mL EtOH was added to the solution for the washing procedure, and after 10 min of centrifugation (4000 rcf), hexane was added to the precipitate until achieving an absorbance of 1.0 at 350 nm. Then, the hexane was evaporated, and 4 mL ODE was added to the precipitate, forming a Ag₂S stock suspension.

Ag₂Se nanoparticles (NPs) synthesis. Ag₂Se NPs were synthesized using a previously published procedure, with some modifications.²⁷ 0.5 g AgNO₃ was mixed in 10 mL ODA at 180 °C for 10 minutes under air; then 120 mg Se was added, and the stirring continued for 10 more min. After cooling to room temperature, the Ag₂Se product was washed several times with EtOH and redispersed in hexane, forming a solution with an absorbance of 1.0 at 473 nm after ×100 dilution. Then, the hexane in 1.5 mL stock solution was evaporated and replaced by 8 mL ODE added to the precipitate, forming a Ag₂Se stock suspension.

Cu₂S nanoparticles synthesis. Cu₂S NPs were synthesized using a previously published procedure, with some modifications.²⁸ 200 mg CuAc₂·2H₂O was mixed in 10 mL DDT under N₂ atmosphere, then the temperature was raised to 220 °C and kept for 30 minutes before cooling to room temperature and washed several times with EtOH. Toluene was added until reaching an absorbance value of 1.0 at 421 nm. The toluene in the stock solution (ca. 3 mL) was evaporated, and 8 mL ODE was added to the precipitate, forming a Cu₂S stock suspension.

CdS nanoparticles synthesis. CdO powder (16 mg) was mixed with 1.5 mL OA and 4 mL ODE under vacuum for 20 min at room temperature; then, the temperature was raised to 120 °C under N₂ atmosphere for 30 min. Then, at 265 °C, 0.87 mL S-ODE solution (10 mg S powder mixed in 3 mL ODE for 2 h at 60 °C) was injected; after 10 minutes incubation at 250 °C the solution cooled down to room temperature and underwent several cycles of washing (using IPA) and redispersion (in 4 mL toluene), forming the Cu₂S stock suspension.

Cs-OA solution preparation. 19.5 mg Cs₂CO₃ and 0.1 mL OA were mixed in 10 mL ODE, held under vacuum for 30 minutes at 120 °C, and then incubated for 15 minutes at 150 °C under an N₂ atmosphere, forming a clear solution. Immediately before use, the solution is heated to 100 °C to allow injection of a liquid clear solution.

PbBr₂ solution preparation. 69 mg PbBr₂ was mixed with 0.5 mL OAm and 0.5 mL OA in 5 mL anhydrous toluene under N₂ atmosphere at 100 °C until dissolving the PbBr₂ salt (∼1.5 h). This solution is diluted ×10 for use in the washing process.

CsPbBr₃ NWs synthesis. PbBr₂ and cesium oleate solutions were prepared separately. 20 mg PbBr₂ was mixed in 5 mL ODE and 1 mL OA at 120 °C under vacuum for one hour as a purification step. Then, after changing the atmosphere to N₂, 0.5 mL dry OAm was injected before raising the temperature to 190 °C; during the heating process, the PbBr₂ salt dissolved, changing the reaction solution's color to a clear yellow; at this point, 0.2 mL Ag₂S/Ag₂Se solution was injected followed by hot (∼100 °C) 0.35 mL Cs-OA solution injection. After 5 minutes, the synthesis was quenched with a water bath, and the solution was centrifuged (8000 rcf) for 5 minutes. 5 mL anhydrous toluene was added to the precipitate, followed by 0.1 mL dry OAm and 0.5 mL PbBr₂ solution, shaken for 2 minutes and centrifuged (4000 rcf) for 6 minutes. The described wash was repeated twice more but without OAm. The resulting precipitate at the end of the washing procedure was finally dispersed in anhydrous toluene for further characterization.

For the Cu₂S-catalyzed CsPbBr₃ NWs synthesis, we use a similar procedure, but with 220 °C reaction temperature and 0.2 mL Cu₂S solution that was injected after the temperature raises back to the 220 °C setpoint after the OAm injection.

In situ XRD experiments. The experimental setup follows the procedure published by our group.²⁹ The reaction mixture was prepared by taking 3 mL of Ag₂S in hexane suspension (absorbance of 1.0 at 421 nm), evaporation of the hexane, followed by addition of 150 μL ODE and mixing for 60 min under N₂ atmosphere. The resulting slurry was placed inside a commercial HTK1200 0.8 mm deep sample carrier. The sample carrier was then placed on the sample holder, which was inserted and fixed inside the environmental heating chamber, which was then purged and filled with He (g) for 30 min. A pre-planned non-ambient program in the Data Collector software (Malvern PANalytical) regulated the temperature of the oven and the timing of the XRD scans. The temperature in the oven chamber was elevated at a heat ramp of 30 °C min⁻¹ for all the measurements performed in a scan window (2θ values) of 39–48° and the scan duration of each pattern was set to 9 min. At each temperature setpoint, the sample remained for 18 minutes, including the measurement and 9 minutes of incubation before.

Characterization

Instruments and techniques. Transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and scanning TEM (STEM) imaging were conducted using a JEOL JEM-2100F analytical TEM operated at 200 keV and equipped with a GATAN 894 US1000 camera.

Energy-dispersive X-ray spectroscopy (EDS) analysis was performed using a JEOL JEM-2100F TEM operated at 200 kV and equipped with an Oxford Instruments X-Max 65T SDD detector. The probe size during the analysis was set to 1 nm. AZtec software (v. 3.3) was used for the EDS data analysis.

High resolution STEM (HRSTEM) imaging was conducted using Spectra 200 (Thermo Fisher Scientific) with a Cs-corrected probe (S-CORR) scanning transmission electron microscope (S/TEM) operated at 200 kV. The images were recorded in STEM mode with a high-angle annular dark field (HAADF) detector.

Ex situ XRD measurements were conducted using Panalytical Empyrean III (Malvern Panalytical) multi-purpose diffractometer equipped with a Cu X-ray source (Cu K_α, λ = 1.5406 Å), operated at 45 kV and 40 mA. The instrument was equipped with the iCore–dCore automated XRD optics combination, a PixCEL 3D detector in 1D line-detector mode. Measurements were recorded of dry samples after drop-casting on (100) single-side polished Si substrates.

In situ XRD measurements were conducted using Panalytical Empyrean (Malvern Panalytical) diffractometer equipped with an X'Celerator detector using Cu K_α radiation (λ = 1.5406 Å), operated at 45 kV and 40 mA recording in Anton Paar's HTK 1200N high-temperature oven chamber with an aluminum oxide sample holder as a sample stage for continuous XRD monitoring at different temperatures. The chamber was filled with He(g) to maintain an inert atmosphere.

UV–vis absorption was measured using an Edinburgh Instruments DS5 dual beam spectrophotometer with tungsten halogen and deuterium light sources and quartz cuvettes with an optical path of 10 mm.

Photoluminescence (PL) spectra were collected using Varian Cary Eclipse fluorimeter, exciting the samples at λ_exc = 410 nm.

Results and discussion

The synthetic process commences by mixing PbBr₂ powder and oleic acid in ODE. Following a purification step under vacuum at 120 °C (as detailed in Experimental section), oleylamine is added to the mixture. As the temperature rises to 190 °C, the mixture changes color to clear yellow due to the complexation of the PbBr₂. Subsequently, Ag₂S NPs (Fig. S1†) dispersion (see full details in the Experimental section) is injected, followed by the injection of a cesium oleate (Cs-OA) solution. After 5 minutes, thin (d ∼5 ± 1 nm, Fig. S2†) NWs with both spherical and cubic tips form, as depicted in the TEM image in Fig. 1a. EDS mapping (Fig. 1b and Fig. S2†) reveals that the spherical tips consist of silver (light blue) and sulfur (green), corresponding to the Ag₂S NPs introduced during synthesis. Meanwhile, the NWs comprise cesium (yellow), lead (purple), and bromine (red).

Fig. 1 Characterization of Ag₂S-catalyzed CsPbBr₃ NWs. (a) TEM image, (b) elemental EDS map—silver in light blue, sulfur in green, cesium in yellow, lead in purple, and bromine in red, and (c) UV–vis absorbance and photoluminescence (PL) spectra in black dotted red lines, respectively (λ_exc = 410 nm). The dark field STEM image and individual elemental maps corresponding to panel (b) appear in Fig. S3.†

The UV–vis absorbance spectrum in Fig. 1c exhibits a peak at 494 nm, characteristic of perovskite CsPbBr₃ NWs, with a corresponding single PL emission peak centered about 511 nm.

Interestingly, although there are Ag₂S NPs on the tip of each NW, their absorbance is not evident in the UV–vis spectrum. This discrepancy can be attributed to the negligible amount of Ag₂S relative to the long CsPbBr₃ NWs, which can reach lengths of 1–2 μm, as observed in the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image in Fig. S4.† nanowires are shown in Fig. 2. The high-resolution TEM (HRTEM) image in Fig. 2a shows the NW's tip with a darker contrast, exhibiting the (122) and (102) crystallographic planes of monoclinic Ag₂S. Further characterizations of the crystallographic structure of the nanowires are shown in Fig. 2. The NW, close to the interface with the Ag₂S NP tip, shows a brighter contrast and displays the (101) planes of the cubic perovskite CsPbBr₃ phase (d₁₀₁ = 4.12 Å). The X-ray diffraction (XRD) pattern (Fig. 2b) corroborates the cubic perovskite CsPbBr₃ phase formation. Notably, the diffractions attributed to (100) and (200) exhibit higher relative intensity compared to the literature bulk diffraction card (red sticks at the bottom of Fig. 2b).

Fig. 2 Crystallographic characterization of Ag₂S-catalyzed CsPbBr₃ NWs. (a) HRTEM image, (b) XRD pattern, and (c) HRSTEM image. The asterisk (*) in the XRD pattern analysis denotes a diffraction from the single-sided polished Si substrate.

This phenomenon is explained by examining the HRSTEM image in Fig. 2c, which depicts CsPbBr₃ NWs with the 〈100〉 growth direction; this orientation of the 1D structure leads to an enhanced relative intensity of the (100) and (200) planes compared to bulk 3D cubic phase.

We attribute the observed growth mechanisms to the SSS mechanism.¹⁹ Ag₂S NPs that serve as catalysts transform from the monoclinic phase at room temperature to the superionic cubic phase at high temperatures (bulk phase transition temperature, T_{tr, bulk} = 179 °C).³⁰ Typically, this mechanism catalyzes the formation of one-dimensional metal chalcogenide NPs.^31–34 Here, we demonstrate the formation of CsPbBr₃ perovskite NWs for the first time using an SSS catalyst-assisted growth mechanism. A control experiment was conducted to validate this by carrying out the synthesis under the same conditions except for adding the Ag₂S NPs. The TEM image of the outcome product of this experiment (Fig. S5†) shows the formation of only typical cubes and 2D sheets of cubic phase CsPbBr₃ with no nanowires. To better understand the effect of the temperature on the nanowires’ formation, we synthesized CsPbBr₃ NWs at 170 °C (lower than the T_{tr, bulk} of Ag₂S). CsPbBr₃ NWs still formed even at this lower temperature (Fig. 3a). This observation indicates that the catalyst is still reactive, which can be attributed to the size effect of the Ag₂S NPs, where the transition temperature is expected to be lower than that of the bulk one.^19,35

Fig. 3 Ag₂S activity as an SSS catalyst as a function of temperature. TEM image of Ag₂S-catalyzed CsPbBr₃ NWs (a) at 170 °C, (b) at 140 °C, and (c) at 120 °C. (d) In situ XRD patterns of Ag₂S NPs in ODE as a function of temperature (in the 110–160 °C range); the asterisks (*) denote diffractions from the corundum crucible in which the measurement was monitored.

For further investigation and study of the catalyst transition temperature effect, CsPbBr₃ nanowires were synthesized at two temperatures (Fig. 3b and c): at 140 °C, we observed a mixture of rectangular nanoparticles and a minor nanowire product, while at 120 °C, only rectangular CsPbBr₃ NPs and unreacted Ag₂S nanoparticles were present. These results show that at 140 °C a partial phase transformation occurs; in contrast, at 120 °C Ag₂S remains inactive since it is below the transformation temperature.

To investigate this transition in the reported system, we performed in situ XRD measurements²⁹ of Ag₂S NPs in ODE (similar conditions to the original synthesis). As shown in Fig. 3d at room temperature (black pattern; bottom), Ag₂S NPs exhibit a monoclinic phase with dominant diffraction signals at 40.7° and 43.3° and a small peak at 45.5°. At 160 °C (blue pattern; top), a complete transformation into the superionic cubic phase occurs, with a single diffraction peak about 2θ = 45.5° attributed to the (211) plane (this position is close to the (112) plane of the monoclinic phase). The phase transition is evident from the changing ratio between the diffraction at 43.3° and 45.5°. At 130 °C (olive green pattern) and above, the experimental diffraction peak at ca. 45.5° becomes similar in intensity to the peak at 43.3°, indicating the partial transformation of some Ag₂S NPs into the cubic phase. The overlap between the two phases increases the experimental intensity at 45.5° until it becomes the dominant peak after complete transformation at 160 °C.

Together with the TEM images (Fig. 3b and c) it confirms that CsPbBr₃ NWs formation is temperature-dependent since the temperature determines Ag₂S's phase, thus its catalytic activity, supporting the CsPbBr₃ NWs growth mechanism being SSS.

One may expect that NWs synthesized via an SSS mechanism, like all catalyst-assisted growth nanowires, would have a catalyst decorating each tip. However, some NWs lack this feature (notably in the TEM images shown in Fig. 3). Yang and colleagues attributed this to the fragile nature of these materials and extensive purification, which can damage and break the NWs in their work on CsPbBr₃ NWs preparation.¹³

We also noticed that the interface between the Ag₂S catalyst and the CsPbBr₃ NW is the weakest point, as shown in Fig. S6.† During image scanning, the HRSTEM image shows a separation between the two domains at the interface. This suggests that NWs without tips are either NW fragments or NWs that have lost their tip before imaging.

A kinetic study confirmed that each NW has a tip (a requirement for an SSS mechanism). In each separate synthesis, the reaction was quenched using a water bath at different times. The first synthesis was quenched immediately after the Cs-OA injection. As demonstrated in Fig. 4a, even after this brief reaction, CsPbBr₃ NWs form, measuring around 100 ± 20 nm (Fig. S2†) in length.

Fig. 4 TEM images of Ag₂S-catalyzed CsPbBr₃ NWs reaction stages at different quenching times: (a) immediate quenching, (b) 5 s, (c) 1 min, and (d) 5 min.

This length allows us to observe both ends of the NWs: each NW has the spherical Ag₂S catalyst on the tip (dark contrast in the TEM image); some NWs have a cube at the other end, which will be discussed later. The short length of these NWs (Fig. 4a) can be explained by the relationship between the reaction temperature and the catalytic activity that we demonstrated in Fig. 3. The quenching process from 190 °C to the inactive 130 °C temperature takes 3–4 seconds, meaning even when reaction quenching is attempted, the catalyst remains active for about 3–4 s, which is sufficient for a 100 nm growth.

In Fig. 4b, where the synthesis was quenched 5 seconds later, the NWs grew to lengths of about 310 ± 90 nm (Fig. S2†). Most of them have a spherical tip supporting the SSS mechanism and a cube on the other side. Fig. S7† shows an HRSTEM image of five distinct NW tips from the same sample presented in Fig. 4b; two of them have the spherical Ag₂S catalyst, and the others exhibit a cube-shaped tip that matches the same CsPbBr₃ perovskite phase as the NW itself. The discussed CsPbBr₃ cube is located opposite to the growth direction, leading us to believe that it forms at the beginning of the reaction. After the fast injection of Cs-OA, we propose that two processes occur concurrently: NW growth via an SSS mechanism and the typical CsPbBr₃ nucleation and growth (‘regular’ growth mechanism). Most self-nucleated CsPbBr₃ are washed out during the washing process, but the newly formed CsPbBr₃ NW tip (via SSS) can also serve as a nucleus for a cube that would form on the older side of each NW by the end of the reaction. Therefore, as expected, the CsPbBr₃ cubes also appear in the longer NWs (longer reaction times shown in Fig. 4c and d) and sometimes even on some NW fragments.

Rogach and co-workers noted that the perovskite CsPbBr₃ crystallization process is very fast and takes 3–10 seconds to form cube-shaped NPs.³⁶ This can explain why some of the short NWs in Fig. 4a do not have cubes on the tips.

During the described quenching process, the 3–10 seconds timeframe—which is required for the cube formation—is sufficient for cooling down the reaction medium to a temperature that prevents some of the cubes from crystallizing. However, these images explain the difference between the tips and show the temporal control over the NW length. Most importantly, they illustrate how fast this catalytic process occurs compared to other synthetic methods yielding CsPbBr₃ NWs.

Thus far, we have demonstrated that Ag₂S NPs can act as catalysts for forming CsPbBr₃ NWs. However, this is not unique to Ag₂S, as other materials with a superionic phase can also catalyze SSS growth. We first replaced Ag₂S with Ag₂Se, another known SSS catalyst. As seen in the TEM image (Fig. 5a), thin NWs with both spherical and cubical tips were formed, similar to those catalyzed by Ag₂S. EDS mapping and spectra (Fig. S8 and S9†) confirm that the spherical Ag₂Se catalyst is linked to the CsPbBr₃ NW. Furthermore, the HRTEM image (Fig. 5b) shows that the darker contrast sphere corresponds to the orthorhombic Ag₂Se phase, while the NW linked to these Ag₂Se NPs is in the cubic perovskite CsPbBr₃ phase. The UV–vis absorbance spectrum of the entire sample also shows the characteristic absorbance of CsPbBr₃ perovskites with a local absorbance maximum at 493 nm and a PL emission at 516 nm (Fig. S10†).

Fig. 5 CsPbBr₃ NWs synthesized with SSS catalysts. (a) TEM and (b) HRTEM images of Ag₂Se-catalyzed NWs. (c) TEM and (d) HRTEM images of Cu₂S-catalyzed NWs.

Additionally, we have used Cu₂S as the SSS catalyst. This experiment aimed to demonstrate the synthesis’ generality and show that the growth is not solely dependent on the presence of silver in the system. For the synthesis with Cu₂S, we increased the reaction temperature to 220 °C to form the NWs (Fig. 5c), which is inconsistent with the simple relationship between the catalytic activity and temperature, as observed and described for the Ag₂S system. The active superionic phase transition of Cu₂S is T_{tr, bulk} = 105 °C;³⁷ however, even at 190 °C, where the Cu₂S is indeed in the active superionic phase, no NWs formed, suggesting that the phase transition is not the only factor affecting the reactivity of SSS catalysts.

The synthesis of the HP NWs using Cu₂S catalyst has a lower yield compared to other two catalyst systems, possibly due to a combination of two reasons: (i) the relatively low reactivity of Cu₂S, as observed in other works,¹⁹ and (ii) at higher temperatures, the self-nucleation process becomes more dominant, consuming the CsPbBr₃ at the expense of the SSS process, which leads to lower NW yield. However, CsPbBr₃ NWs form in the presence of a Cu₂S catalyst, as shown in Fig. 5d; the darker contrast monoclinic Cu₂S phase tip connects to a CsPbBr₃ cubic perovskite phase NW, as expected from an SSS growth. The quantitative EDS spectra in Fig. S11† corroborate this analysis. To further prove the necessity of the superionic phase, we conducted a control experiment and replaced the catalyst with cubic CdS NPs (Fig. S12a†), keeping all other experimental conditions the same. As shown in Fig. S12b,† no NWs formed. This suggests that a requirement for a cubic phase or a chalcogenide material from a NP is not sufficient to allow CsPbBr₃ NWs growth; an active superionic phase (such as Ag₂S, Ag₂Se, or Cu₂S) is required for a successful catalyst-assisted SSS NW growth.

Conclusion

In conclusion, we have devised a novel approach to synthesize CsPbBr₃ perovskite NWs using a catalyst-assisted growth mechanism. For the first time, we have synthesized CsPbBr₃ perovskite NWs using superionic Ag₂S NPs as a growth catalyst—a previously employed technique for 1D metal chalcogenides materials preparation. We have demonstrated the growth kinetics, highlighting the catalytic process’ speed. We have also illustrated how the phase transition of the catalyst at varying temperatures influences the final product and how versatile this method is by employing other known superionic SSS catalysts (specifically, Ag₂Se and Cu₂S). This technique paves a new way for forming HP NWs, demonstrating that these materials can be produced using catalyst-assisted growth methods such as solution–liquid–solid and vapor–liquid–solid.^38,39 We envision that such catalyst-assisted growth methods would be beneficial for forming hybrid nanostructures that incorporate these HPs,^24,34 or for fabricating arrays that can be integrated into devices.⁴⁰

Data availability

The data supporting this article have been included as part of the ESI. COD (XRD) card numbers, additional (S)TEM images and EDS, UV–vis and PL data.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the Israeli Science Foundation (ISF, grant no. 1507/22). The authors thank Dr Vladimir Ezersky for helpful discussions and for high-resolution and analytical TEM. K. S. thanks the chemo-tech fellowship from the Kreitman School of Advanced Graduate Studies, Ben-Gurion University of the Negev, and the Council for Higher Education fellowship for outstanding doctoral students from the Arab community.

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Footnote

† Electronic supplementary information (ESI) available: COD (XRD) card numbers, additional (S)TEM images and EDS, UV–vis and PL data. See DOI: https://doi.org/10.1039/d4nr03158j

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