Modulating phase distribution and passivating surface defects of quasi-2D perovskites via potassium tetrafluoroborate for light-emitting diodes

Abstract

Quasi-two-dimensional (quasi-2D) perovskites show high potential for perovskite LEDs (PeLEDs) due to a bit larger exciton binding energy and favorable energy transfer as a result of the natural quantum well structure. However, various-n phases and a large number of surface defects within the quasi-2D perovskites generally result in unfavorable energy transfer and serious nonradiative recombination during the electroluminescence (EL) of PeLEDs. Herein, potassium tetrafluoroborate (KBF4) is applied to fine modulate the phase distribution and simultaneously reduce the defect density of quasi-2D perovskites. The results reveal that the introduction of BF4- ions into the quasi-2D perovskites substantially suppresses the nucleation of small-n phases and induces the nucleation of intermediate-n phases to realize an effective cascade carrier transfer, which could accelerate the carrier transfer from small-n phases to high-n phases within the quasi-2D perovskites. Meanwhile, BF4- ions could also fill the Br- anion vacancies of the quasi-2D perovskites to diminish the nonradiative recombination. Consequently, the PeLED shows the maximum external quantum efficiency (EQE) of 13.92% with a high luminance of 19882 cd m−2. This work provides a new avenue to manipulate the phase distribution and defect passivation of quasi-2D perovskites for high-performance PeLEDs.