Exploring the Design Rules for Efficient Metal Halide Perovskite Light Emitting Diodes

Defect passivation, through decreasing nonradiative recombination rate, has long been considered as the key to efficient perovskite light emitting diodes (LEDs). Here, by revisiting the two commonly used defect passivation strategies, stochiometric ratio tuning and additive engineering, in various perovskite systems, we found its limitations in explaining the superior high performance in light emitting. Surprisingly, a different mechanism other than defect passivation is proved to be responsible for efficient perovskite LEDs. Our low-temperature photoluminescence and ultraviolet photoelectron spectroscopy (UPS) results indicate that these strategies lead to increment of shallow traps and thus p-dope the perovskites. Such p-doping largely enhances the photoluminescence quantum efficiency especially at low carrier density region and can even go beyond 90%. Through carrier dynamics analysis, we point out that the dominant factor responsible for high efficiency in perovskites is the enhancement of radiative recombination via doping rather than defect passivation. Furthermore, this p-doping effect is verified by special device design where poor hole injection results in high external quantum efficiency of perovskite light emitting diodes (PeLEDs). Our discoveries provide design rules to fabricate high-efficiency PeLEDs.