Molecular Chemistry-Controlled Hybrid Ink-Derived\nEfficient Cu₂ZnSnS₄ Photocathodes for Photoelectrochemical\nWater Splitting

Abstract

To realize economically competitive\nhydrogen production through\nphotoelectrochemical (PEC) water splitting, it is essential to develop\nan efficient photoelectrode consisting of earth-abundant constituents\nin conjunction with low-cost solution processing. Cu₂ZnSnS₄ (CZTS) has received significant attention as a promising\nphotocathode owing to its abundance and good absorption properties.\nHowever, the efficiency of the solution-processed CZTS photocathode\nis not yet comparable to its counterparts. Here, a hybrid ink, obtained\nby careful control of precursor mixing order, was used to produce\na highly efficient CZTS photocathode. The molecular chemistry-controlled\nhybrid ink formulation, particularly the roles of thiourea–Sn²⁺ complexation, was elucidated by liquid Raman spectroscopy.\nThe hybrid ink-derived CZTS thin films modified with conformal coating\nof an n-type TiO₂/CdS double layer and a Pt electrocatalyst\nachieved an exceptionally high photocurrent of 13 mA cm^–2 at −0.2 V versus a reversible hydrogen electrode\nunder 1 sun illumination. The modified photocathodes showed relatively\nstable H₂ production with faradaic efficiency close to\nunity.