Weak exciton–phonon coupling in two-dimensional perovskite thin films for high-performance UV photodetection

Two-dimensional layered hybrid perovskites are promising materials for UV–Vis photodetectors owing to their self-assembled quantum-well structure, low-temperature processing, and low defect density. Here we investigate how crystalline order in PEA2PbBr4 thin films deposited by bar coating and spin coating on flexible substrates affects exciton–phonon coupling and UV photodetection. Bar-coated films exhibit higher structural order and lower microstrain, forming extended, well-connected domains that promote in-plane transport. Under near ultraviolet illumination the bar coated devices reach responsivity around 40 mA W−1 and specific detectivity above 1013 Jones at low flux while preserving ultra-low dark current. Temperature-dependent photoluminescence combined with current–voltage measurements consistently link these improved device metrics to reduced inhomogeneous broadening, weaker exciton–phonon coupling for the delocalized excitonic transition and a larger carrier lifetime-to-transit-time ratio in bar-coated films. These results demonstrate that controlling film formation via bar coating enables the engineering of crystalline order and exciton–phonon interactions, leading to UV photodetector performance approaching that of PEA2PbBr4 single crystals in a fully solution-processed, flexible architecture. Two-dimensional layered hybrid perovskites show strong potential for UV–Vis photodetectors due to their favorable optoelectronic properties. Here, the authors show that bar coating enhances crystalline order, yielding high-performance UV photodetectors with near-single-crystal performance.