Composition-Dependent Photoelectrochemical Properties of Nonstoichiometric Cu2ZnSnS4 Nanoparticles

Size-quantized Cu–Zn–Sn–S quaternary semiconductor nanoparticles having various chemical compositions were synthesized by a solution-phase synthesis method. The chemical composition of the resulting nanoparticles could be controlled by changing the molar fractions of Cu, Zn, and Sn ions in the preparation. The resulting particles had an average particle diameter of 2–3 nm with a tetragonal crystal structure. Their energy gap was enlarged with an increase in Zn content in the particles in the range of 0.98–1.69 eV. Cu–Zn–Sn–S nanoparticles immobilized on ITO electrodes behaved as a p-type semiconductor, in which onset potential of the cathodic photocurrent was ca. +0.25 V vs Ag/AgCl, being independent of the chemical composition. The electronic energy structure of particles, determined from photoelectrochemical measurements, was composed of a valence band edge at ca. +0.25 V vs Ag/AgCl, the potential of which was not influenced by the chemical composition of particles, and a conduction band edge that was negatively shifted from −0.72 to −1.37 V vs Ag/AgCl by increasing Zn content in the particles. Interestingly, the incident photon-to-current efficiency (IPCE) depended on the chemical composition, especially on the Cu/Sn ratio in the particles, and the optimum value was obtained for nonstoichiometric Cu 2 ZnSnS 4 nanoparticles with Cu- and Zn-poor composition.