Ligand compensation enabling efficient and stable exciton recombination in perovskite QDs for high-performance QLEDs

Perovskite quantum dot-based light-emitting diodes (QLEDs) have been considered as a promising luminescent technology due to high color purity and wide color gamut. However, the realization of high-performance QLED is still hindered by near-perfect quantum dots (QDs) with efficient and stable exciton recombination behavior. Here, we proposed a ligand compensation (LC) strategy to optimize the QDs by introducing a ligand pair of tri-n-octylphosphine (TOP) and CsBr. The ligand pair could enhance the clarity and colloidal stability of the QD ink, facilitating the fabrication of highly smooth films. On one hand, TOP engages in interactions with Pb and effectively passivates the surface uncoordinated Pb2+. On the other hand, the supplement of CsBr provides a Br-rich environment to reduce Br vacancies (VBr). Through LC, QD films possess a high photoluminescence quantum efficiency of 82% and a shallow hole level, which enables efficient exciton recombination. In addition, the LC makes QD films exhibit stable exciton combination behavior and electrical transport characteristics. Resultantly, the LC-optimized QLEDs show a maximum external quantum efficiency (EQE) of 24.7% and an operational lifetime T50 of 182 h at an initial luminance of 100 cd m-2, which is obviously higher than that of the control device (EQE of 15.8%, T50 of 11 h). The proposed LC strategy for optimizing perovskite QDs presents a novel concept for achieving high-performance QLEDs and holds great potential for widespread application in various optoelectronics.