Studying the effect of the controlled off-stoichiometry on the properties of Zn₂SnO₄ nanoparticles for DSSC applications

In this paper, the influence of off-stoichiometry and annealing temperature on the structural, electrical and optical properties of the zinc stannate nanoparticles prepared by conventional solid-state reaction method were studied. The structural studies revealed that the phase purity of the synthesized nanoparticles increases with annealing temperature. Furthermore, the reduction of the molar ratio of ZnO to SnO₂ from 2 to 1.8 increased the electrical conductivity of the nanoparticles. The electrical conductivity improvement was ascribed to the excess Sn atoms in the nanoparticles which can fill the place of zinc atoms (Zn²⁺) or occupy interstitial sites in the zinc stannate lattice and lead to creation of more free electrons. Subsequently, the resultant nanoparticles were used as photoanode material. The fabricated dye-sensitized solar cells with 1.8 molar ratio of ZnO to SnO₂ displayed better photovoltaic performance. Dye loading measurement on the Zn₂SnO₄-based photoelectrode revealed that the excess Sn in this structure not only increases the electrical conductivity of the Zn₂SnO₄ nanoparticles but also enhances their dye loading.