Phase Engineering for Highly Efficient Quasi-Two-Dimensional All-Inorganic Perovskite Light-Emitting Diodes via Adjusting the Ratio of Cs Cation

Quasi-two-dimensional (2D) perovskites have received intensive attention as a new class of luminescent materials owing to large exciton binding energy and high photoluminescence efficiency. However, there usually contains a mixture of phases in these materials, and excessive low-dimensional phase perovskite is harmful for luminescence efficiency owing to the strong exciton-phonon quenching at the room temperature. Herein, a simple and effective method is proposed to suppress the growth of low-dimensional phase components in quasi-2D perovskite film via carefully adjusting the molar ratio of cesium bromide (CsBr) and phenylpropylammonium bromide (PPABr). The device based on this optimized film has achieved a peak brightness of 2921 cd m(−2) and peak current efficiency of 1.38 cd A(−1), far away higher than that of the pristine CsPbBr(3) device. This research proves a new way for modulating the phase composition in quasi-2D perovskites to fabricate highly efficient perovskite light-emitting diodes (PeLEDs).