Trivalent Ni oxidation controlled through regulating lithium content to minimize perovskite interfacial recombination

Organic–inorganic hybrid perovskite solar cells,one of the most promising photovoltaic devices,have made great progress in their efficiency and preparation technology.In this study,uniform,highly conductive Li_(n)NiO_(x)(0≤n≤1;0<x≤3)films were prepared by electrochemical deposition for a range of Li concentration.Photovoltaic performance for the perovskite solar cells was enhanced through incorporation of the ion pair of Ni^(3+)-Ni^(2+) as the interfacial passivation.Depending on the amount of lithium doping,controlled interfacial oxidation was induced by Ni^(3+).The Li_(0.32)NiO_(x)inhibited charge recombination,reduced the defect density,and enhanced the photocurrent density.A maximum power conversion efficiency of 20.44%was obtained by Li_(0.32)NiO_(x).Further,in the long-term,in-air stabilities of unencapsulated Li_(n)-NiO_(x) perovskite solar cells were demonstrated.