High-pressure exciton engineering in two-dimensional metal halide perovskite toward intense deep-blue emission and regulated photocurrent property

Exciton engineering in two-dimensional (2D) hybrid metal halide perovskites (HMHPs) is crucial for optimizing photoluminescent (PL) and photocurrent (PC) properties, yet it remains a great challenge. In this work, high pressure is applied to accurately control the conversion equilibrium among free carriers (FCs), free excitons (FEs), and trapped excitons in 2D HMHPs of 10% Pb2+-doped BDACdBr4 (BDA = 1, 4-butanediamine). Initial compression induces noticeable interlayer approach and limited intralayer distortion. Reduced self-trapping energy facilitates reverse intersystem crossing of self-trapped excitons (STEs), leading to visible PL transformation from STE to FE emission. Under sufficient compression, phase transition occurs, and significant structural distortions are accompanied by further exciton release. The FE emission is enhanced with more symmetric line shape, achieving intense deep-blue emission that meets the international specification of deep-blue display. Sufficiently decreased binding energy also promotes the dissociation of FEs to simultaneously enhance PC property.