Trap‐State Suppression via Dual Defect Healing Enables Stable Near‐Infrared Lanthanide‐Based Quantum Dot LEDs

Abstract Lanthanide‐alloyed perovskite quantum dots (QDs, Yb 3+ : CsPb(Cl 1‐x Br x ) 3 ) are promising in near‐infrared light‐emitting diodes (NIR‐LEDs) for theoretically ≈200% photoluminance quantum yield because of quantum‐cutting effect, where one high‐energy photon is used as a source to generate two low‐energy photons. However, the inferior stability of Yb 3+ : CsPb(Cl 1‐x Br x ) 3 remains a big challenge. It is posited that vacancy‐defect complexes during lanthanide ions alloying are the driving force behind the collapse of octahedral geometry. Here, a coordination agent compensation plus an in situ doping strategy is developed to address the incompatibility between high NIR emission and good stability. This is achieved by combining the sodium ion to fill the vacancy and a coordinating agent (pyridine‐2‐carboxylic acid) for passivation. This enabled the treated QD films to have a magnitude of order decreased deep trap density compared to the control. Besides, the treated composite exhibits a sixfold increase in NIR intensity and tenfold lower trap states. Using the optimized Yb 3 ⁺: CsPb(Cl 1‐x Br x ) 3 , NIR‐LEDs are fabricated and achieved an external quantum efficiency of 8.2%, one of the highest values among NIR LEDs with emission >950 nm. Furthermore, these LEDs exhibit a 30‐fold increase in operational stability compared to the control.