Superior External Quantum Efficiency of LEDs via Quasi-2D Perovskite Crystals Implanted with Phenethylammonium Acetate.

The multiple quantum well structure of a quasi-two-dimensional (quasi-2D) perovskite leads to nonradiative Auger recombination (AR). This is due to high local carrier density in recombination centers, although the radiative recombination is improved by efficient energy transfer. In this study, we suppress the AR by introducing phenethylammonium acetate (PEAAc) into the quasi-2D PEA 2 Cs n -1 Pb n Br 3 n +1 perovskite. The recombination centers of n ≥ 4 phases can be promoted because the COO - preferentially coordinates with Pb 2+ , inhibiting the fast formation of n = 1, 2, 3 phases with phenethylammonium anion (PEA + ). Thus, the AR is suppressed due to the lower density of local charge carriers. To balance the AR suppression and decreasing binding energy in promoting the n ≥ 4 phases, the PEAAc:PEABr molar ratios are adjusted. At the optimal molar ratio, perovskite light-emitting diodes (PeLEDs) with a maximum luminescence of ∼29942 cd m -2 and a maximum external quantum efficiency of ∼20.2% are achieved. These results confirm the most efficient PeLEDs based on PEA 2 Cs n -1 Pb n Br 3 n +1 without passivation. Moreover, the efficiency roll off is significantly mitigated with a high threshold of over 3.51 mA/cm 2 . This study develops high-efficiency PeLEDs with a low efficiency rolloff.