Stable, Efficient Red Perovskite Light-Emitting Diodes by (alpha, delta)-CsPbI3 Phase Engineering

Recently, inorganic cesium-lead halide perovskites with high thermal stability have attracted much attention as promising light-emitting material for research of perovskite-based light-emitting diodes (PeLEDs) toward high-definition displays. However, the CsPbI3-based red PeLEDs still suffer low external quantum efficiency (EQE) and poor device stability due to the spontaneous phase transition from cubic CsPbI3 (alpha-CsPbI3) to nonradiative orthorhombic phase (delta-CsPbI3) under ambient conditions. Here, a feasible approach is reported on phase engineering by incorporating the long-chain cation (e.g., 2-(naphthalene-1-yl)ethanamine (NEA)) in CsPbI3 for stable and high-performance CsPbI3-based red light-emitting diodes (LEDs). A high EQE of 8.65% is successfully achieved for the characteristic red emission at approximate to 682 nm representing the highest value among Cs-based red PeLEDs up to now. More importantly, the corresponding PeLEDs exhibit outstanding stability with EQE retaining 90% after 3 months of storage. These results verify the potential of using cesium-based inorganic perovskite as viable alternatives to methylammonium (MA)- or formamidinium (FA)-based perovskite for desirable practical applications.