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.

Sustainable Mixed-Halide Perovskite Resistive Switching Memories Using Self-Assembled Monolayers as the Bottom Contact

“…Finally, the functional/terminal group determines the properties and surface morphology of the resulting ultrathin film, enabling tunable functionality depending on the chemical group used, which can lead to several device applications. As a consequence, SAM molecules can improve the interface properties with the resulting perovskite film, thus passivating interfacial defects. , These properties extend the application of SAMs in electronic devices such as LEDs, transistors, solar cells, and sensors . In addition, SAM molecules are able to reduce traps and voids in the perovskite layer resulting to enhanced interface properties when compared to the perovskite films grown on PTAA. − SAM molecules are also successfully employed in large-area devices. ,− Common SAM molecules used in PSCs include [2-(3,6-dimethoxy-9 H -carbazol-9-yl)­ethyl]­phosphonic acid (MeO-2PACz) and [2-(9 H -carbazol-9-yl)­ethyl]­phosphonic acid, although other derivatives have been developed as well. ,, …”