Nanoscale Photo-Absorbing Kesterite Grown on Anatase Mesoscopic Films by Sequential Binary Chalcogenide Solution Deposition-Exchange, Annealing, and Etching

Cu₂ZnSnS₄ (CZTS) with kesterite crystal structure is considered a promising semiconductor material for photovoltaics due to its excellent optical properties and nontoxic, earth-abundant components. In this work, the nanoscale coating of CZTS on anatase mesoscopic films is studied to build an absorber (kesterite)-conductor (anatase) photoanode structure with high composition uniformity - a challenge for complex absorbers like quaternary CZTS. To this end, we first develop a three-step binary chalcogenide solution deposition-exchange sequence for precursor preparation that is followed by in-depth analysis of the deposit-forming chemical reactions and characterization of elemental distribution and composition control. Then, crystallization is induced by annealing at 500 °C for 1 h, followed by an additional hydrochloric acid etching step to remove secondary binary phases and surface imperfections leading to improved composition of a CZTS/TiO₂ film as a candidate for use in kesterite-sensitized solar cells.