Molecular Chemistry-Controlled Hybrid Ink Derived Efficient Cu2ZnSnS4 Photocathodes for Photoelectrochemical Water Splitting

To realize economically competitive hydrogen production through photoelectrochemical (PEC) water splitting, it is essential to develop an efficient photoelectrode consisting of earth-abundant constituents in conjunction with low-cost solution processing. Cu2ZnSnS4 (CZTS) has received significant attention as a promising photocathode owing to its abundance and good absorption properties. However, the efficiency of the solution-processed CZTS photocathode is not yet comparable to its counterparts. Here, a hybrid ink, obtained by careful control of precursor mixing order, was used to produce a highly efficient CZTS photocathode. The molecular chemistry-controlled hybrid ink formulation, particularly the roles of thiourea-Sn2+ complexation, was elucidated by liquid Raman spectroscopy. The hybrid ink-derived CZTS thin films modified with conformal coating of an n-type TiO2/CdS double layer and a Pt electrocatalyst achieved an exceptionally high photocurrent of 13 mA cm(-2) at-0.2 V versus a reversible hydrogen electrode under 1 sun illumination. The modified photocathodes showed relatively stable H-2 production with faradaic efficiency close to unity.