Chlorine distribution management for spectrally stable and efficient perovskite blue light-emitting diodes

Blue emitting perovskite electroluminescent (EL) devices are mainly realized based on chlorine mixing in bromide perovskites including CsPbBr₃, CH₃NH₃PbBr₃ (MAPbBr₃), and CH(NH₂)₂PbBr₃ (FAPbBr₃). However, the inhomogeneous distribution and varied mobility of Cl⁻ and Br⁻ ions in alloyed perovskite films always result in EL spectra gradually shifting from blue to green region during device operation. Herein, alloyed FAPbBr_3−xCl_x nanocrystal (NC) films with optimized Cl distribution are fabricated through employment of Cl terminated amine ligands (Cl-ligands). The as fabricated FAPbBr_3−xCl_x NC films exhibit a Cl rich surface and 9 nm blue shifted emission spectrum compared to FAPbBr_3−xCl_x films fabricated by conventional Br terminated ligands (Br-ligands). Furthermore, EL devices based on Cl-ligands achieve blue EL emissions with maximum luminance of 2810 cd/m² and EQE of 3.1%, which is almost three times higher than that of EL devices based on Br-ligands. Importantly, Cl-ligands derived EL devices show greatly enhanced spectra stability with only slightly red-shifted EL spectra during device operation in a wide bias range, providing an alternative strategy for spectrally stable perovskite blue light-emitting diodes.