Boosting the Photocurrent Density of p‑Type Solar Cells Based on Organometal Halide Perovskite-Sensitized Mesoporous NiO Photocathodes

Abstract

The p–n tandem design of a sensitized solar cell is a novel concept holding the potential to overcome the efficiency limitation of conventional single-junction sensitized solar cells. Significant improvement of the photocurrent density (<i>J</i>_sc) of the p-type half-cell is a prerequisite for the realization of a highly efficient p–n tandem cell in the future. This study has demonstrated effective photocathodes based on novel organometal halide perovskite-sensitized mesoporous NiO in liquid-electrolyte-based p-type solar cells. An acceptably high <i>J</i>_sc up to 9.47 mA cm^–2 and efficiency up to 0.71% have been achieved on the basis of the CH₃NH₃PbI₃/NiO solar cell at 100 mW cm^–2 light intensity, which are significantly higher than those of any previously reported liquid-electrolyte-based p-type solar cells based on sensitizers of organic dyes or inorganic quantum dots. The dense blocking layer made by spray pyrolysis of nickel acetylacetonate holds the key to determining the current flow direction of the solar cells. High hole injection efficiency at the perovskite/NiO interface and high hole collection efficiency through the mesoporous NiO network have been proved by time-resolved photoluminescence and transient photocurrent/photovoltage decay measurements. The limitation of these p-type solar cells primarily rests with the adverse light absorption by the NiO mesoporous film; the secondary limitation arises from the highly viscous ethyl acetate-based electrolyte, which is helpful for the solar cell stability but hinders fluent diffusion into the pore channels, giving rise to a nonlinear dependence of <i>J</i>_sc on the light intensity