High stability and strong luminescence CsPbBr₃-Cs₄PbBr₆ thin films for all-inorganic perovskite light-emitting diodes

All-inorganic lead halide perovskite, characterized by its exceptional optical and electrical properties, is burgeoning as a potential optoelectronic material. However, the standalone CsPbBr₃ component encounters several challenges including small exciton binding energy (≈40 meV) and long charge diffusion length, giving rise to low photo-luminescence quantum-yield (PLQY); ion migration leads to instability in device operation, hindering device operation and potential development. To circumvent these limitations, our research endeavors to construct a novel core-shell structure that transforms the continuous [PbX₆]^4- octahedron into an isolated octahedral structure. We introduce the Cs₄PbBr₆ phase with 0D structure to passivate the vacancy defects in CsPbBr₃, thereby suppressing ion migration and enhancing the luminescence intensity and stability. Our methodology involves fabricating dense CsPbBr₃-Cs₄PbBr₆ composite films using a co-evaporation method, wherein the molar ratio of CsBr and PbBr₂ is precisely adjusted. The films are subsequently rapidly annealed under ambient air conditions, and the effects of different annealing temperatures and annealing times on the CsPbBr₃-Cs₄PbBr₆ films were investigated. Our results demonstrate significantly improved stability of the annealed films, with a mere 15% decrease in PL intensity after 100 days of storage under ambient air conditions at 48% relative humidity (RH). Based on this thin film, we fabricated all-inorganic structure Ag/N-Si/CsPbBr₃-Cs₄PbBr₆/NiO/ITO light emitting diodes (LEDs), the devices have a low turn-on voltage V_T ∼3 V and under unencapsulated, ambient air conditions, it can operate continuously for 12 hours under DC drive with only 10% attenuation. The results we obtained open up the possibility of designing and developing air-stable perovskite LEDs.