Energetic Disorder Mitigation of Hole-Transport Layers via Molecular Assembly Boosts Charge Transport to Unlock Efficient and Stable Perovskite Light-Emitting Devices.

Abstract

Inadequate understanding and poor control of energetic disorder in polymer charge-transport layers pose a significant barrier to the device efficiency and stability of a perovskite light-emitting diode (PeLED). Here, we report a molecular monolayer engineering strategy to reduce the energetic disorder of poly(9-vinylcarbazole) (PVK), a widely used hole-transport material. By introducing a self-assembled monolayer (SAM) of [2-(9<i>H</i>-carbazol-9-yl)ethyl]phosphonic acid (2PACz), we promote ordered π-π stacking in the overlying PVK film, resulting in prolonged coherence lengths, as demonstrated by grazing-incidence wide-angle X-ray scattering. We adapted ultraviolet photoelectron spectroscopy and an energy-resolved electrochemical impedance spectroscopy approach, which reliably tracks energetic disorders. PeLEDs employing SAM-modified PVK layers exhibit significantly improved external quantum efficiency (EQE) of 30.4% and a 9-fold prolonged operational lifetime. The successful application to blue PeLEDs (λ = 485 nm; EQE improved from 15.5% to 25.3%) underscores the broad applicability of this disorder-engineering strategy across diverse emitters.