NiO_x mesoporous films derived from Ni(OH)₂ nanosheets for perovskite solar cells

A mesoporous NiO_x (m-NiO_x) film which is deposited from a precursor using solution-derived Ni(OH)₂ nanosheets as the starting material is employed as the hole transport layer to fabricate the perovskite solar cell. A simple annealing process at 500 °C in air decomposes the Ni(OH)₂ nanosheets into NiO_x nanoparticles, removes organic components, and produces nanopores in the film, leading to the formation of m-NiO_x films at once. Results indicate that the annealing time has a great effect on the morphology and crystallinity of the resulting m-NiO_x films, and prolonging the annealing time leads to smaller NiO_x nanoparticles, bigger pores and higher crystallinity, which contribute to a better device performance. After a careful optimization, the highest power conversion efficiency of 11.97% is achieved on the device based on the m-NiO_x film annealed at 500 °C for 3 h. This work provides a new method to prepare efficient m-NiO_x films for high performance perovskite solar cells.