Switchable synthesis of p- and n-type Cu–In–S grooved pyramid-like microcrystals for unassisted photoelectrochemical water splitting

Abstract

Herein, p- and n-type switchable Cu–In–S microcrystals with a grooved pyramid-like morphology are facilely synthesized by transforming binary In₂S₃. A cation exchange and in situ growth mechanism is proposed to illustrate the generation of grooved pyramid-like Cu–In–S samples. It is demonstrated that the structure, composition, and semiconducting properties of Cu–In–S films could be controlled by maneuvering the rate of cation exchange, which can be simply adjusted by varying the amount of the sulfur precursor. With an increased amount of added thiourea, p-type CuInS₂ and n-type CuIn₅S₈ as well as a mixture of CuInS₂ and CuIn₅S₈ are prepared. The p-type CuInS₂ and n-type CuIn₅S₈ photoelectrodes respectively exhibit a cathodic photocurrent of −0.18 mA cm⁻² at −0.4 V vs. RHE and an anodic photocurrent of 0.61 mA cm⁻² at 0.7 V vs. RHE in 0.1 M Na₂SO₄ solution (pH = 3) under AM 1.5G illumination. More importantly, an unassisted water splitting system in parallel mode composed of a CoO_x/CuIn₅S₈ photoanode and a Pt/CuInS₂ photocathode is constructed, which shows a photocurrent density of 0.015 mA cm⁻². The present work could provide a new idea for constructing efficient unassisted photoelectrochemical water splitting devices using copper-based chalcogenides. Meanwhile, the capability to switch p–n semiconducting properties provides a great inspiration to enable the development of novel semiconductor materials for photoelectric applications.