Optimizing the band alignment of p-Si based heterojunction photocathode for photoelectrochemical hydrogen production

Constructing p-Si based heterojunction photocathode is a promising means to convert solar energy into storable hydrogen fuel . The favorable energy band alignment between p-Si absorber and electron transport layer (ETL) is crucial to realize efficient photogenerated carrier separation and transport during photoelectrochemical water splitting . The trade-off between large Fermi level difference and optimized conduction band offset (CBO) in p-Si heterojunction is a major limiting factor for achieving high solar-to-hydrogen efficiency. Herein, we introduced a double CdS/In 2 S 3 ETLs on p-Si to optimize band alignment and facilitate the charge carrier transport at the interface. The p-Si/CdS/In 2 S 3 system presents a step-like energy band alignment and the appropriate CBO at p-Si/CdS (0.46 eV) and CdS/In 2 S 3 (0.25 eV) interface suppress the charge recombination and efficiently extract photogenerated electrons. The Electrochemical impedance spectroscopy measurement shows a lower charge transfer resistance for the double ETLs compared with the single ETL counterparts. As a result, the p-Si/CdS/In 2 S 3 /Pt photoelectrode exhibits a positive onset potential of ∼0.5 V RHE and a high applied bias photo-to-current efficiency of 5.6 % under AM 1.5G illumination. The strategy of band alignment engineering provides an effective way to improve the device performance and can be extended to other emerging semiconductor thin film photocathodes.