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

Formamidinium lead bromide perovskite (FAPbBr₃) nanocrystals have attracted increasing attention due to their greener photoluminescence (PL) and higher thermal stability in comparison to more popular methylammonium lead bromide perovskite (MAPbBr₃). Here we proposed a facile and highly reproducible room-temperature method for the preparation of few-layer (1–4) two-dimensional (2D) FAPbBr₃ 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 FAPbBr₃ 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 FAPbBr₃ 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 MAPbBr₃ nanocrystals-based LEDs in air; the half lifetime T50 of our devices was about 5 times longer than that of MAPbBr₃ nanocrystals-based LEDs. This work demonstrates the great potential of FAPbBr₃ NPs in light-emitting devices for future ultrahigh-resolution displays.