Selective etching of metastable phase induced an efficient CuIn0.7Ga0.3S2 nano-photocathode for solar water splitting

A p-n tandem photoelectrochemical water splitting cell is considered as a promising low-cost technique to convert solar energy into hydrogen. A p type CuIn0.7Ga0.3S2 is an attractive photocathode with a high photocurrent onset potential. However, it is still a key challenge to explore an efficient CuIn0.7Ga0.3S2 photocathode. Two kinds of impurities, CuxS and a metastable CuAu ordering phase, usually exist in CuIn1-xGaxS2, which are both considered to be harmful to the performance of CuIn1-xGaxS2-based solar conversion devices. However, in this study, the photocurrent of a CuIn0.7Ga0.3S2 nano-photocathode is significantly enhanced by selective electrochemical etching of a CuAu ordering phase, but not increased after etching of CuxS. Moreover, having been further coated with CdS and Pt co-catalyst, a Pt/CdS/CuIn0.7Ga0.3S2 nano-photocathode exhibits a high solar photocurrent density of 6.0 mA cm(-2) at 0 V-RHE under AM 1.5G simulated sunlight (100 mW cm(-2)) irradiation, which is comparable with the highest recorded photocurrent on a Pt/CdS/CuIn1-xGaxS2 microcrystal photocathode. This strategy will be helpful to explore other efficient Cu-chalcopyrite solar conversion devices.