Ultrahigh-efficiency quantum dot light-emitting diodes through ligand reconstruction

Abstract Steric hindrance of long-chain ligands leads to abundant unpassivated dangling bonds on quantum dots (QDs), which significantly impair the efficiency and operational stability of QD light-emitting diodes (QLEDs), especially in ultra-small pixel devices. Here, we utilize a small molecule with strong coordination capability, zirconium acetylacetonate (Zr(acac)4), to precisely repatch the residual surface defects of QDs. The acetylacetonate anions with high agility and flexibility can overcome the obstacles of spatial hindrance imposed by long-chain ligands, readily diffuse to the surface of QDs and strongly anchor onto the unsaturated zinc. This reconstruction enhances quantum yield of QDs and suppresses exciton quenching typically at the QD/ZnO interface. Additionally, the injection of excessive carriers is suppressed, preventing electron leakage to the hole transport layer (HTL). Consequently, the optimized pixel-less QLEDs achieve an ultrahigh external quantum efficiency (EQE) of 34.3% and an operational T95@1000 cd/m2 lifetime of 19,450 h, which are markedly superior to the unmodified counterparts (EQE = 27.5%, T95@1000 cd/m2 = 4974 h). The resultant high-resolution QLEDs exhibit a champion-level EQE of 25.3% at approximately 10,000 pixels per inch (PPI).