Homogenized NiO nanoparticles for improved hole transport in inverted perovskite solar cells

The power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs) is still lagging behind that of conventional PSCs, in part because of inefficient carrier transport and poor morphology of hole transport layers (HTLs). We optimized self-assembly of [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) onto nickel oxide (NiO) nanoparticles as an HTL through treatment with hydrogen peroxide, which created a more uniform dispersion of nanoparticles with high conductivity attributed to the formation of Ni³⁺ as well as surface hydroxyl groups for bonding. A 25.2% certified PCE for a mask size of 0.074 square centimeters was obtained. This device maintained 85.4% of the initial PCE after 1000 hours of stabilized power output operation under 1 sun light irradiation at about 50°C and 85.1% of the initial PCE after 500 hours of accelerated aging at 85°C. We obtained a PCE of 21.0% for a minimodule with an aperture area of 14.65 square centimeters.