Improving the stability of all‐inorganic halide perovskite nanocrystals has become an urgent task that cannot be ignored in practical applications. Lead halide perovskite CsPbX3 (X = Br, I, Cl) compounds are considered as the potential materials for next‐generation light‐emitting devices due to their superior optical properties. However, they are threatened by thermal degradation and atmospheric moisture. In order to better solve this practical problem, CsPbBr3 quantum dots (QDs) and CsPbBr3@Cs4PbBr6 nanocrystals (NCs) are tested under heating and cooling cycles, and the photoluminescence (PL) intensity loss of different perovskite materials at high temperatures is investigated. In addition, a thermoplastic polyurethane encapsulation strategy is proposed to improve their properties of thermal degradation and moisture resistance. This inexpensive and convenient method not only greatly reduces the PL intensity loss, but also shows excellent PL performance even in water. The encapsulated material has both flexible and elastic properties, which paves the way for the next commercial processing of all inorganic perovskite materials.

Ensuring the stability of all‐inorganic halide perovskite light‐emitting diodes (LEDs) has become an obstacle that needs to be broken for commercial applications. Currently, lead halide perovskite CsPbX3 (X = Br, I, Cl) nanocrystals (NCs) are considered as alternative materials for future fluorescent lighting devices due to their combination of superior optical and electronic properties. However, the temperature of the surface of the LEDs will increase after long‐term power‐on work, which greatly affects the optical stability of CsPbX3 NCs. In order to overcome this bottleneck issue, a strategy of annealing perovskite materials in liquid is proposed, and the changes in photoluminescence and electroluminescence (EL) behaviors before and after annealing are studied. The results show that the luminescence stability of the annealed perovskite materials is significantly improved. Moreover, the EL stability of different perovskite LED devices under long‐term operation is monitored, and the performance of the annealed materials is particularly outstanding. The results have proved that this convenient and low‐cost liquid annealing strategy is suitable for large‐scale postprocessing of perovskite materials, granting them stable fluorescence emission, which will bring a new dawn to the commercialization of next‐generation optoelectronic devices.

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Exploring a convenient method to solve the stability problem of all-inorganic halide perovskite nanocrystals (NCs) has become an urgent task in their practical application. In recent years, cesium lead halide perovskite CsPbX 3 (X = Cl, Br, and I) NCs, as the star material for the development of next-generation optoelectronic devices, have stimulated tremendous interest due to their excellent optical and electronic properties. Unfortunately, the performance of CsPbX 3 NCs will become impaired due to interference from the external environment. Here, a convenient one-pot method was proposed, and the transition of CsPbBr 3 quantum dots to two-dimensional CsPbBr 3 /CsPb 2 Br 5 composite plates (CPs) was achieved by adjusting the reaction time. Largescale octagonal CsPbBr 3 /CsPb 2 Br 5 CPs were quickly obtained, and the morphology and phase transition in the entire reaction time period were explored. Subsequently, the products obtained at different reaction times were evaluated for long-term storage stability under air conditions, and the results showed that the CsPbBr 3 /CsPb 2 Br 5 CPs exhibited excellent photoluminescence stability. The proposed preparation method presents a convenient way to improve the stability of CsPbX 3 with low cost. On the other hand, by incorporating these products into thermoplastic polyurethane (TPU), a waterproof ink material that can be written directly was realized, where CsPbBr 3 /CsPb 2 Br 5 /TPU waterproof composite ink exhibits excellent stability and recyclability under aqueous solutions at different temperatures, which will provide a new choice for the commercial development of perovskite. KEYWORDS: cesium lead halide perovskite, CsPbBr 3 quantum dots, CsPbBr 3 /CsPb 2 Br 5 composite plates, photoluminescence stability, waterproof composite ink

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