The anticipated redox reaction induced by the nickel oxide transport layer with perovskite in perovskite-based light-emitting diodes

The application of NiOx hole transport layer induces an electrochemical reaction in the contact interface with organolead halide perovskite, causing the reduction of Pb(II) to the metallic Pb. The formation of metallic lead atoms, as characterized by the measurement of X-ray photoelectron spectroscopy, quenches the electroluminescence (EL) in perovskite-based light-emitting diodes (PeLEDs). However, during the electric bias of PeLEDs, the magnitude of photoluminescence (PL) increases by 7 times of the perovskite active layer, which is correlated with the reversed electrochemical reaction of metallic Pb in NiOx/perovskite interface. This would be the origin for the observation of EL magnitude overshoot in the initial bias of PeLEDs. Introducing an additional buffer layer at the interface preventing the direct contact of NiOx hole transport layer with the perovskite layer inhibits the interfacial electrochemical reaction. Our results elucidate the unanticipated redox reaction induced by NiOx hole transport layer at the contact interface with perovskite, being one of the key components to modulate device performance and cause EL overshoot of PeLEDs.