Revealing the Influence of Hole Transport Layer on the Stability of Blue Quantum Dot Light-Emitting Diodes

Abstract

High-performance blue quantum-dot light-emitting diodes (QLEDs) typically employ poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) as the hole transport layer (HTL). However, the insufficient energy barrier between the LUMO of TFB and the conduction band of blue QDs (BQDs) induces severe electron leakage, resulting in parasitic interfacial emission and compromised device stability. Herein, we investigate the structural evolution and optoelectronic degradation of TFB films during QLED aging via a charge functional layer peeling technique. We reveal that oxidation reactions occur both at the TFB/BQDs interface and within the bulk TFB film under operational stress. Driven by leaked electrons, the main and side chains of TFB molecules undergo scission and oxidation, generating abundant carrier traps associated with oxidation products (C2H3O+, C2H3O2+) and molecular fragments (C3H5+, C4H7+, C5H9+). Furthermore, this structural degradation downshifts the conduction band level of the TFB layer by 0.21 eV, thereby exacerbating electron leakage. Concurrently, the diminished hole mobility disrupts the carrier balance and increases exciton density in the emissive layer. This work elucidates the intrinsic HTL degradation mechanism in state-of-the-art QLEDs, providing critical insights for designing highly stable blue QLED devices.