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

Abstract

A series of Ni_1−xMg_xO (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 (V_oc) of the solar cell. The overall power conversion efficiency is optimized for the Ni_0.9Mg_0.1O photocathode, which is significantly improved by about 85% from pure NiO. The enhanced performance is attributed to 34.4% increased photocurrent density (J_sc), 22.5% increased V_oc, 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 Ni_0.8Mg_0.2O, the valance band position is too deep and hinders efficient hole injection. J_sc of the corresponding solar cell decreases largely. This work proves that Ni_0.9Mg_0.1O is a superior alternative to NiO as a photocathode material in p-type DSCs.