High‐performance pure-red light‐emitting diodes based on CsPbBr_xI_3-x–multi-ligands–KBr composite films

Metal halide perovskites have been extensively investigated for application in light-emitting diodes (LEDs) because their optical band gap can be adjusted via the alteration of their halide-ion composition. However, the performance of metal halide perovskite LEDs (PeLEDs) is limited by halide-vacancy-induced surface defects. Therefore, mixed-halide perovskites were introduced to prevent the formation of halide vacancies on the perovskite surface. However, typical CsPbBr_xI_3‑x-based PeLEDs exhibit ion migration under an electrical field, which results in phase segregation and the deterioration of the device performance. In this study, to overcome these obstacles, PeLEDs based on CsPbBr_xI_3-x–multi-ligands–KBr films were introduced. The use of multi-ligands could facilitate the recombination of excitons and stabilization of the α-phase perovskite crystals. Moreover, the KBr not only prevented the formation of halide vacancies by interaction with excess halide ions but also improved the surface coverage. Thus, an optimized film-based—CsPbBr_xI_3-x–multi-ligand (70% NMABr_0.7I_0.3–15% N,N-dimethyl-1,3-propanediammonium bromide–15% 1,3-propanediammonium bromide)–KBr (0.03 M)—PeLED was fabricated, which had a current density of 5.1 mA/cm², current efficiency of 3.2 cd/A, luminance of 743.2 cd/m², and an external quantum efficiency of 10.2%. Moreover, this PeLED exhibited a low turn-on voltage (1.6 V) with pure-red emission.