Optical and surface probe investigation of secondary phases in Cu₂ZnSnS₄ films grown by electrochemical deposition

Abstract Cu₂ZnSnS₄ (CZTS) films were grown by electrochemical deposition, and we measured the work function of the as-grown and of the KCN-etched CZTS surfaces by using Kelvin probe force microscopy (KPFM) and micro-Raman scattering spectroscopy with incident laser wavelengths of 488.0 and 632.8 nm, respectively, and the results indicate that a secondary phase formed at different depths. The KPFM measurements can discriminate phase uniformity at the nano-scale. Secondary phases, such as Cu_2-xS (0<x<1), ZnS, and MoS₂, were identified on the as-grown surface while Cu_2-xS was removed from the KCN-etched surface. The KCN-etched CZTS absorption layer was measured to have a 5.0% conversion efficiency. Owing to the low cost of electrochemical deposition, it is desirable to obtain high tailored CZTS films can be obtained with the robust surface characteristics of a uniform work function with a single phase.