Bright and efficient light-emitting diodes based on perovskite quantum dots with formamidine-methylamine hybrid cations

Perovskites have become an excellent candidate for the next-generation optoelectronic semiconductor materials due to their attractive optoelectronic properties, such as size-dependent emission peak, narrow emission spectrum, and high luminescent efficiency. Herein, we present the synthesis of mixed-cation perovskite quantum dots (QDs) based on FA(x)MA((1-x))PbBr(3) (FA = CH(NH2)(2), MA = CH3NH2). By photoluminescence (PL) characterization, it shows that the perovskite QDs emit green light (similar to 530 nm) and measured high absolute quantum yield up to 88%. It is also found that the emission peak shows a blue-shift with the increase of MA(+) doping due to a contracted lattice structure. We also fabricated perovskite light-emitting diodes (PeLEDs) with FA(x)MA((1-x))PbBr(3) as the light-emitting layer. Ultraviolet photoelectron spectroscopy confirmed that the valence band of FA(x)MA((1-x))PbBr(3) decreases with MA content increases, which can reduce the hole injection barrier in related devices. As a result, we obtained light-emitting diodes with an optimized composition of synthesized materials FA(0.8)MA(0.1)PbBr(3) as the emitting layer exhibiting maximum luminance of 2020 cd . m(-2), a maximum current efficiency of 14.10 cd . A(-1) and an external quantum efficiency of 3.36%, which are more than two-fold that of the FAPbBr(3) PeLED, indicating that the doping of methylamine cations in FA-cation-based perovskites is a beneficial way to improve device performance.