Few-layer formamidinium lead bromide nanoplatelets for ultrapure-green and high-efficiency light-emitting diodes

Formamidinium lead bromide perovskite (FAPbBr(3)) nanocrystals have attracted increasing attention due to their greener photoluminescence (PL) and higher thermal stability in comparison to more popular methylammonium lead bromide perovskite (MAPbBr(3)). Here we proposed a facile and highly reproducible room-temperature method for the preparation of few-layer (1-4) two-dimensional (2D) FAPbBr(3) nanoplatelets (NPs) with ultrapure green PL at 532 nm and high photoluminescence quantum yield (PLQY) of 88%. High-efficiency ultrapure green light-emitting diodes (LEDs) based on the few-layer 2D FAPbBr(3) NPs were further demonstrated. The LEDs showed a maximum current efficiency (CE) of 15.31 cd/A and an external quantum efficiency (EQE) of 3.53%, which are significantly better than the FAPbBr3 polycrystalline film-based LEDs reported so far. Significantly, the 2D FAPbBr(3) NPs-based LEDs exhibited an ultrapure-green color emission that could cover 97% of the Recommendation 2020 (Rec. 2020) color standard and 114% of the national television system committee (NTSC) standard in the CIE 1931 color space. Moreover, the devices possessed a much better stability than the MAPbBr(3) nanocrystals-based LEDs in air; the half lifetime T50 of our devices was about 5 times longer than that of MAPbBr(3) nanocrystals-based LEDs. This work demonstrates the great potential of FAPbBr(3) NPs in light-emitting devices for future ultrahigh-resolution displays.