# Unanticipated Interfacial Redox Reaction in the NiOx Transport Layer of Perovskite Light‐Emitting Diodes

## TL;DR

A redox reaction between nickel oxide and perovskite layers in light-emitting diodes causes instability, but adding an interlayer prevents this reaction and improves performance.

## Contribution

Discovery of an unanticipated redox reaction at the NiOx-perovskite interface and a solution using an interlayer to suppress it.

## Key findings

- XPS confirms Ni0 oxidation and Pb2+ reduction at the NiOx-perovskite interface.
- An interlayer like PVK suppresses redox reactions and reduces luminescence quenching.
- Interfacial modification stabilizes trap distribution and mitigates EL overshoot.

## Abstract

This study reveals an unanticipated interfacial redox reaction between the nickel oxide (NiOx) hole transport layer and perovskite active layer in organolead halide perovskite light‐emitting diodes (PeLEDs). Specifically, metallic nickel (Ni0) present in the NiOx layer undergoes oxidation while lead ions (Pb2+) from the perovskite precursor are reduced, forming nickel (II) ions (Ni2+) and metallic lead (Pb0), as confirmed by X‐ray photoelectron spectroscopy (XPS). The formation of Pb0, a well‐known luminescence quenching center, is correlated with the significantly suppressed photoluminescence (PL) before biasing and the pronounced electroluminescence (EL) overshoot observed at the onset of electrical excitation. Introduction of an electrode interlayer, such as a polyvinyl carbazole (PVK), prevents direct contact between NiOx and the perovskite, thereby effectively suppressing the detrimental redox reaction between them. This electrode interfacial modification eliminates Pb° formation, mitigates luminescence quenching, and suppresses EL overshoot. Moreover, the trap density at the perovskite interface is substantially reduced, and the deep trap distribution remains stable under bias. The findings offer critical insights into bias‐induced luminescence enhancement phenomena and present a reliable, scalable strategy to mitigate these phenomena, contributing to the development of advanced PeLEDs.

This study presents the unanticipated interfacial redox reaction between NiOx and perovskite, which is characterized by XPS. This redox reaction is one of the primary reasons for the bias‐induced instability of PeLEDs and is particularly suppressed by simply applying an interface layer between NiOx and perovskite.