Phosphonic-Acid-Functionalized Polymer for Bright and Spectrally Stable Blue Perovskite Light-Emitting Diodes

Abstract

Blue perovskite light-emitting diodes (PeLEDs) have progressed rapidly in external quantum efficiency (EQE), gradually narrowing the performance gap with their green and red counterparts. However, high efficiencies have so far been realized mainly at low brightness, while achieving spectrally stable blue emission with appreciable efficiency at high brightness remains a major challenge. These limitations primarily arise from inefficient hole injection caused by the deep valence band and the intrinsic phase instability of heavily Br/Cl-mixed perovskites. Here, we report ultrabright and spectrally stable blue PeLEDs by employing a phosphonic-acid-functionalized carbazole-fluorene copolymer with a deep-lying highest occupied molecular orbital (HOMO) level as a hole-selective transport layer. Our strategy simultaneously raises the work function of the bottom NiOx contact and modulates the surface wettability, thereby enabling efficient hole injection and governing the perovskite crystallization to form high-quality emissive films. The corresponding blue PeLEDs achieve a peak luminance of ∼2.9 × 104 cd m–2 while maintaining excellent spectral stability under harsh driving conditions up to a current density exceeding 2,800 mA cm–2 (with luminance sustained above 1 × 104 cd m–2). Furthermore, with a pulsed voltage operation, a maximum luminance of up to 3.4 × 105 cd m–2 is attained. This work provides an effective interfacial material design strategy for realizing high-brightness blue PeLEDs.