Origin and Suppression of External Quantum Efficiency Roll-Off in Quasi-Two-Dimensional Metal Halide Perovskite Light-Emitting Diodes

Metal halide perovskites are promising as the emitter of efficient light-emitting diodes (LEDs). External quantum efficiencies (EQEs) of perovskite LEDs (Pe-LEDs) have already surpassed 20%, which is comparable to those of state-of-the-art organic LEDs. However, one of the issues remaining in Pe-LEDs is a very large roll-off of EQEs at high current densities. Thus, it is necessary to suppress this EQE roll-off through the clarification of its mechanisms. One possible reason for the EQE roll-off is expected to be Auger recombination, which is a nonradiative process involving three charge carriers (one excited state and one carrier in this case). Herein, we report that Auger recombination is accelerated by holes trapped in Pe-LEDs. Thermally stimulated current measurements reveal that defect levels inside the perovskite’s bandgap are deeper for the holes than for the electrons. Therefore, the holes trapped by the deeper defect states strongly interact with the perovskite’s excited states, causing Auger recombination and the EQE roll-off to occur in Pe-LEDs. Our findings obtained in this study provide a better understanding of the EQE roll-off and can be used to fabricate Pe-LEDs with smaller or negligible EQE roll-off in the future.