Mitigating Ligand Entanglement in Perovskite Quantum Dots for High-Efficiency and Stable Red Light-Emitting Diodes

Achieving simultaneously high efficiency and thermal stability in perovskite quantum dot light-emitting diodes (PeLEDs) requires fundamentally rethinking surface ligand design. Conventional OAm-OA ligands inadequately passivate halide vacancies, causing defect-induced exciton quenching and low efficiency. Beyond this limitation, we reveal for the first time that thermal field triggers ligand entanglement at the atomic scale, which destabilizes the N─H passivation network, induces ligand desorption, and causes rapid stability degradation. This previously unrecognized failure mechanism underscores the need for thermally stable ligand architectures. Herein, we developed a novel stabilization strategy using PFBA ligands that can simultaneously enhance the efficiency and thermal stability of CsPbI₃ QDs. Specifically, PFBA effectively passivates I vacancies and suppresses LO phonon-exciton coupling to enhance the radiative recombination efficiency. Simultaneously, PFBA ligands with rigid fluorinated architectures effectively mitigate thermally induced ligand entanglement, while significantly enhancing OAm-QD binding energy from -1.15 to -3.54 eV through charge-sharing interactions. This approach yields CsPbI₃ QDs exhibiting a 93% PLQY, a 27.1% peak EQE, and 22.8 h of T₅₀, representing 1.3, 1.8, and 16.3-fold improvements over controls, respectively. This study establishes simultaneous suppression of defect-mediated exciton loss and ligand entanglement as a unified design principle for high-efficiency and stable PeLEDs.