Dual function of a high-contrast hydrophobic-hydrophilic coating for enhanced stability of perovskite solar cells in extremely humid environments

In spite of a continuous increase in their power conversion efficiency （PCE） and an economically viable fabrication process,organic-inorganic perovskite solar cells （PSCs） pose a significant problem when used in practical applications：They show fast degradation of the PCE when exposed to very humid environments.In this study,the stability of PSCs under very humid conditions is greatly enhanced by coating the surface of the PSC devices with a multi-layer film consisting of ultrahydrophobic and relatively hydrophilic layers.A hydrophobic composite of poly（methyl methacrylate） （PMMA）,polyurethane （PU）,and SiO2 nanoparticles successfully retards the water molecules from very humid surroundings.Also,the hydrophilic layer with moderately PMMA captures the residual moisture within the perovskite layer;subsequently,the perovskite layer recovers.This dual function of the coating film keeps the PCE of PSCs at 17.3% for 180 min when exposed to over 95% humidity.

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%.