Controlled oxidation of Ni for stress-free hole transport layer of large-scale perovskite solar cells

The effect of the residual thermal stress of NiO films on the performance of an inverted type perovskite solar cell was studied.In this study,NiO films were grown on fluorine dopedtin oxide(FTO)substrates of different surface roughness by thermally oxidizing Ni film and weretested as a hole transport layer for large-scale perovskite solar cells.Experimental and simulation results show that it is very important tosuppress the appearance of the residual stress at the NiO-FTO in terface during the oxidation of the Ni film for effective hole extracti on.The Ni oxidation on the flat FTO film produced in-plane compressive stress in the NiO film due to the Ni film volume expansion.This led to theformation of defects including small blisters.These residual stress and defects in creased leakage curre nt through the NiO film,preve ntingholes from being selectively collected at the NiO-perovskite interface.However,when Ni was deposited and oxidized on the rough surface,the residual stress of the NiO film was negligible and its inhere nt high resistance was maintained.Stress-free NiO film is an excelle nt holetransport layer that stops the photogenerated electrons of the perovskite layer from moving to FTO.The improvements in the structural andelectrical qualities of the NiO film by engirteering the residual stress reduce the carrier recombination and increase the power conversi onefficiency of the perovskite solar cells to 16.37%.