Zn₂SnO₄-Based Dye-Sensitized Solar Cells: Insight into Dye-Selectivity and Photoelectric Behaviors

Infrared dyes in dye-sensitized solar cells (DSCs) usually mismatch with the band structure of TiO_2. This mismatch subsequently results in insufficient kinetics in charge separation. Researchers have started focusing on ternary oxide semiconductors because of their stability. Moreover, the chemical compositions and band structures of these semiconductors are easy to control. In this paper, a ternary semiconductor oxide, Zn₂SnO₄, was synthesized through a hydrothermal method and used as a photoanode for DSCs. Zn₂SnO₄ selectivity toward organic and ruthenium complex dyes was different from that of TiO₂. Zn₂SnO₄–DSCs performance was improved at a greater degree with organic sensitizer 2-cyano-3-{4-[2-(4- diphenylamino-phenyl)-vinyl]-phenyl}-acrylic acid (TPC) than with cis-bis (isothiocyanato)-bis (2,2-bipyridyl- 4,4-dicarboxylato) ruthenium (II) bis-tetrabutyl-ammonium (N719). We further improved the power conversion efficiency of Zn₂SnO₄-DSCs to 5.72% through surface modification and structural optimization. Stepped light-induced measurement of photocurrent and photovoltage was used to systematically study electron behaviors in surface-modified and unmodified Zn₂SnO₄-based and TiO₂-based DSCs. Zn₂SnO₄ exhibited higher electron diffusion coefficient than TiO₂. The electron lifetime of Zn₂SnO₄-based DSCs increased after surface modification