Preparation and photoelectrochemical properties of densely immobilized Cu2ZnSnS4 nanoparticle films

Colloidal Cu2ZnSnS4 (CZTS) nanoparticles with sizes of 5–6 nm that contain no highly toxic elements were successfully synthesized through thermal reactions of metal acetate and sulfur in high-temperature oleylamine solution. The reaction temperature was a key factor for the synthesis of CZTS nanoparticles: synthesis at temperatures higher than 240 °C gave a pure CZTS crystal phase, whereas a secondary phase of CuS was formed at reaction temperatures lower than 180 °C. Nanoparticles were successfully accumulated on ITO-coated or quartz glass substrates via layer-by-layer deposition using 1,2-ethanedithiol as a cross-linking agent. The resulting CZTS particle films exhibited a photoresponse similar to that of p-type semiconductor photoelectrodes in an aqueous solution containing Eu(NO3)3 as an electron scavenger. Potentials of the valence band edge and conduction band edge were determined from the onset potential of the cathodic photocurrent to be +0.3 and −1.2 V vs. Ag/AgCl, respectively.