Enhanced performance of p-type dye sensitized solar cells based on mesoporous Ni1−xMgxO ternary oxide films

A series of Ni1−xMgxO (x = 0–0.2) oxide mesoporous films with p-type semi-conductivity prepared by surfactant directed self-assembly method have been successfully applied as photocathodes in a p-type dye sensitized solar cell (DSC) system. By gradually increasing the Mg content from 0 to 20% in the ternary oxides, the effective light harvesting efficiency increases monotonically, which is associated with the increased dye absorbing amount and improved optical transmittance, meanwhile the flat-band potential gradually increases, implying a continuous negative shift of the valance band position of the p-type semiconductors. The latter is closely related to the charge injection from dye to semiconductor and the photovoltage (Voc) of the solar cell. The overall power conversion efficiency is optimized for the Ni0.9Mg0.1O photocathode, which is significantly improved by about 85% from pure NiO. The enhanced performance is attributed to 34.4% increased photocurrent density (Jsc), 22.5% increased Voc, and 13.0% increased fill factor. These improvements can be explained by increased light harvesting, enhanced charge collection, and flat-band potential positive shift. On further increasing the Mg content in the ternary oxide to Ni0.8Mg0.2O, the valance band position is too deep and hinders efficient hole injection. Jsc of the corresponding solar cell decreases largely. This work proves that Ni0.9Mg0.1O is a superior alternative to NiO as a photocathode material in p-type DSCs.