Influence of CuI hole transport layer on CuBi2O4 photocathode for photoelectrochemical water splitting

Abstract

Photoelectrochemical water splitting (PEC) is one of the most promising strategies to produce green hydrogen fuels from solar energy. CuBi2O4 (CBO) is attracting p-type semiconductor materials as a photocathode because it has a suitable bandgap for water splitting (~1.8 eV). CBO has an unusual positive photocurrent onset potential (>1 V vs RHE), which can generate a large internal photo-voltage and can contribute the optimization of the solar to hydrogen efficiency. [4-6] Nevertheless, major challenges in the PEC performance of CBO photocathode are well-known as their poor charge carrier transport properties. To overcome this problem, a CuI hole transport layer was adopted in the CBO photocathode to form a type-Ⅱ heterojunction for improving charge transport properties. In this study, CuI/CBO thin films were fabricated by spin coating method on FTO glass substrate. As a result, the CuI/CBO photocathode showed a photocurrent density of -0.707 mA cm-2 at 0.2 VRHE, which was more than four times higher than that of CBO photocathode (-0.173 mA cm-2 at 0.2VRHE). This improvement in PEC performance is expected to be due to band alignment favorable to water splitting, which enhances hole carrier transport properties and suppresses charge recombination.