π-Conjugated molecule-based self-assembled monolayers enable high-efficiency pure-blue perovskite LEDs

Abstract

The hole-injecting interface is crucial for achieving high optoelectronic performance of perovskite light-emitting diodes (PeLEDs), as it lowers the energy barrier between the anode and perovskite emitting layers (EMLs), facilitates efficient hole-carrier extraction, suppresses recombination, and supports growth of highly crystalline perovskite EMLs. However, the widely used hole injection layer (HIL), poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS), has inherent limitations such as low work function, high acidity, and susceptibility to corrosion, the self-assembled monolayers (SAMs) with functional groups have emerged as promising alternatives to PEDOT:PSS for hole-injecting interfaces. In this study, 4PADCB, a phosphonic acid-based SAM with extended π-conjugation, is applied to prepare high-performance pure blue PeLEDs. The 4PADCB provides robust interfacial properties including excellent electrical and morphological characteristics by close interaction with perovskite lattices, demonstrating pure-blue electroluminescence of PeLEDs at 472 nm with a low turn-on voltage (3.20 V) and a peak external quantum efficiency (EQE) of 4.26 %, a fourfold improvement over PEDOT:PSS-based control devices. This enhancement is attributed to reduced interfacial defects and improved carrier injection balance, leading to efficient radiative recombination kinetics. These results highlight the potential of highly conjugated SAMs as innovative components for hole-injecting interfaces, enabling significant advances in PeLED efficiency and stability.