Insulator as Efficient Hole Injection Layer in Perovskite Light‐Emitting Device via MIS Contact

Abstract Polymer insulator is employed as efficient hole injection layer (HIL) in lead halide perovskites light‐emitting diodes (PeLEDs) for the first time, by revealing that metal–insulator–semiconductor (MIS) contact is responsible for the hole‐injection mechanism in PeLEDs with indium tin oxide (ITO)/insulator/perovskite structure. For MIS contact of ITO/insulator/perovskite, the electric field is concentrated in the insulator layer, thereby reducing the tunneling distance from ITO to perovskite. By studying the transient current response, it is confirmed that the accumulation of both electrons and ions at the insulator/perovskite interface is responsible for the screening of electric field. With polystyrene (PS) as hole injection layer, the device exhibits a much better device performance than that of PeLEDs with regular polyvinylcarbazole (PVK) HIL, even though the resistivity of PS is 5 orders of magnitude higher than that of PVK, which confirms the universal applicability of MIS contact. By optimizing the thickness of PS layer, the performance of FAPbBr₃‐based device achieves a turn‐on voltage of 2.8 V, a peak luminous efficiency of 44.7 cd A⁻¹, and an external quantum efficiency of 10.6%.