Double Passivation Using Ultra‐Thin Insulators for Improved Stability and Efficiency of Quasi‐2D Perovskite Light Emitting Diodes

Abstract Interface engineering is a critical parameter for optimal optoelectronic device performance. In quasi‐2D perovskite light emitting diodes (PeLEDs), traditional poly (3,4‐ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) hole injection layer (HIL) is replaced by self‐assembled monolayer (SAM) [2‐(3,6‐dibromo‐9H‐carbazol‐9‐yl) ethyl] phosphonic acid (Br‐2PACz) HIL. The deep highest occupied molecular orbital (HOMO @ −5.73 eV) of Br‐2PACz facilitates the efficient hole‐injection along with a reduction in leakage current by 4–5 orders of magnitude as compared to PEDOT:PSS (HOMO @ −5.00 eV) HIL based optimized PeLEDs. Ultra‐thin SAM‐based Br‐2PACz HIL presents two challenges: i) device reproducibility is hindered by spatial inhomogeneity, and ii) it fails to regulate nonradiative recombination at the perovskite/HIL interface. To address these challenges, the ultra‐thin interlayer of atomic layer deposited aluminum oxide (Al₂O₃) is utilized between Br‐2PACz, and perovskite which aids in passivating the interfacial states at the HIL/perovskite interface. With the optimized thickness of Al₂O₃ interlayer (3 nm), the device's external quantum efficiency (EQE) improved from 9.47% to 13.14%, accompanied by luminous efficiency of 42.8 cd A⁻¹. An ultra‐thin interlayer of lithium fluoride (LiF) (2 nm) is implemented on the top side of the perovskite, which can provide 1.5 times increase in the device's LT₅₀ stability.