Effect of surface modification of nickel oxide hole-transport layer via self-assembled monolayers in perovskite solar cells

Self-assembled monolayers of para-substituted phenylphosphonic acids were used to modify the surface of nickel oxide layer, which served as the hole-transport layer in the fabrication of inverted perovskite solar cells. The monolayer was installed to modulate the work function of NiOx based on their electron-withdrawing or electron-donating substituent, while the perovskite film morphology and quality were not significantly altered due to analogous hydrophilic nature of the modified surfaces. The modification impacted the device performance such that the best-performing device was observed with electron-withdrawing cyano-substituted phosphonic acid modification, with a maximum power conversion efficiency of 18.45% obtained. The effect of modification on parameters such as open-circuit voltage, short-circuit current, and field factor are discussed.