Role of Br-Cl distribution uniformity on the spectral stability of blue emitting mixed-halide perovskites

One of the commonly-held beliefs in quasi-two-dimensional (quasi-2D) bromo-chloride (Br-Cl) mixed-halide perovskite light-emitting diodes (PeLEDs) is that defects are responsible for the poor external quantum efficiency (EQE) and the spectral instability. In our contribution, it's discovered that though the universally employed organic ammonium halide p-F-PEABr enhances EQE, it impairs the spectral stability of the mixed-halide PeLEDs. Further studies have revealed that doping p-F-PEABr into perovskite forms a low-dimensional phase with high Cl-content and a 3D phase with low Cl-content, resulting in a non-uniform Br-Cl distribution. It's demonstrated that the non-uniform distribution of Br-Cl mainly accounts for the spectral instability. The early works which attributed the spectral instability to defects alone unintentionally overlooked the reduction of the low-dimensional phase accompanying the defect passivation. Using organic ammonium halides with weak coordination ability, such as DEABr and DEACl, to passivate defects, can maintain the uniformity of the Br-Cl distribution by preventing the formation of the low-dimensional phase. As a result, both the EQE and spectral stability are enhanced.