Exploration and Optimization of the Polymer-Modified NiO x Hole Transport Layer for Fabricating Inverted Perovskite Solar Cells.

The recombination of charge carriers at the interface between carrier transport layers such as nickel oxide (NiO x ) and the perovskite absorber has long been a challenge in perovskite solar cells (PSCs). To address this issue, we introduced a polymer additive poly(vinyl butyral) into NiO x and subjected it to high-temperature annealing to form a void-containing structure. The formation of voids is confirmed to increase light transmittance and surface area of NiO x , which is beneficial for light absorption and carrier separation within PSCs. Experimental results demonstrate that the incorporation of the polymer additive helped to enhance the hole conductivity and carrier extraction of NiO x with a higher Ni 3+ /Ni 2+ ratio. This also optimized the energy levels of NiO x to match with the perovskite to raise the open-circuit voltage to 1.01 V. By incorporating an additional NiO x layer beneath the polymer-modified NiO x , the device efficiency was further increased as verified from the dark current measurement of devices.