Solution-processed CsPbBr3 perovskite films via CsBr intercalated PbBr2 intermediate for high-performance photodetectors towards underwater wireless optical communication

All inorganic CsPbBr3 perovskite is regarded as a promising candidate of halide perovskites and has attracted great attention due to its superior optoelectronic properties and stability. However, the low and unbalanced solubility of precursors and uncontrollable crystallization result in poor coverage and impurity phases in CsPbBr3 polycrystalline films, hindering the application in optoelectronic devices. In this work, a facile CsBr intercalated nanostructured intermediate based two-step method is reported for simultaneously achieving good morphology and pure phase of CsPbBr3 films. With the CsBr intercalation, the intermediate films deposited in the first step exhibit porous nanostructure and CsxPb2Br4+x crystal phase. This unique porous morphology and crystal structure favor CsBr solution penetration and Cs+ ion diffusion. First-principles calculations are conducted to investigate the phase diagram of intermediates and the diffusion kinetics of Cs+ ions in the various polymorphs. The key role of CsBr intercalation is confirmed for achieving high-quality CsPbBr3 perovskite films with features of pinhole free, pure phase, large grains, and high crystallinity. Photodetectors based on optimized CsPbBr3 films exhibit excellent performance with a peak EQE of 83%, responsivity of 0.35 A/W, and specific detectivity of 1.25×1013 Jones. Fast response speed is also achieved with rise/fall time of 1.41 μs and 2.06 μs and -3 dB bandwidth up to 800 kHz. Moreover, CsPbBr3 PD shows great potential in the application of underwater wireless optical communication due to its low background noise current under ambient light illumination. Overall, this work paves the way for further research on optoelectronic devices and their applications based on CsPbBr3 films.