Composition-Dependent Photoelectrochemical Properties\nof Nonstoichiometric Cu₂ZnSnS₄ Nanoparticles

Abstract

Size-quantized Cu–Zn–Sn–S\nquaternary semiconductor\nnanoparticles having various chemical compositions were synthesized\nby a solution-phase synthesis method. The chemical composition of\nthe resulting nanoparticles could be controlled by changing the molar\nfractions of Cu, Zn, and Sn ions in the preparation. The resulting\nparticles had an average particle diameter of 2–3 nm with a\ntetragonal crystal structure. Their energy gap was enlarged with an\nincrease in Zn content in the particles in the range of 0.98–1.69\neV. Cu–Zn–Sn–S nanoparticles immobilized on ITO\nelectrodes behaved as a p-type semiconductor, in which onset potential\nof the cathodic photocurrent was ca. +0.25 V vs Ag/AgCl, being independent\nof the chemical composition. The electronic energy structure of particles,\ndetermined from photoelectrochemical measurements, was composed of\na valence band edge at ca. +0.25 V vs Ag/AgCl, the potential of which\nwas not influenced by the chemical composition of particles, and a\nconduction band edge that was negatively shifted from −0.72\nto −1.37 V vs Ag/AgCl by increasing Zn content in the particles.\nInterestingly, the incident photon-to-current efficiency (IPCE) depended\non the chemical composition, especially on the Cu/Sn ratio in the\nparticles, and the optimum value was obtained for nonstoichiometric\nCu₂ZnSnS₄ nanoparticles with Cu- and Zn-poor\ncomposition.