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Description
Two-dimensional layered hybrid perovskites are promising candidates for UV-visible photodetection due to their tunable bandgap, high absorption coefficients, and excellent environmental stability. However, the influence of processing methods on fundamental excitonic properties and device performance remains poorly understood. In this work, we demonstrate that the deposition technique fundamentally determines the degree of crystalline order, the strength of exciton–phonon coupling, and ultimately the photodetection regime in PEA2PbBr4-based flexible UV photodetectors.
We compare two solution-processing methods (spin coating and bar coating) applied to the fabrication of PEA2PbBr4 thin films on flexible polyimide substrates. Structural characterization by X-ray diffraction reveals that bar-coated films exhibit sharper diffraction peaks, reduced microstrain, and larger crystalline domains compared to spin-coated films. Optical microscopy confirms improved morphological homogeneity with fewer grain boundaries and better domain connectivity in bar-coated samples.
Temperature-dependent photoluminescence spectroscopy in the 80–300 K range provides direct evidence of the impact of processing on excitonic properties. At low temperatures, both samples develop a distinct double-peak structure corresponding to localized (low-energy, LE) and delocalized (high-energy, HE) excitonic states. However, the analysis of temperature-dependent linewidth broadening reveals striking differences. In bar-coated films, the effective exciton–phonon coupling constant for the HE excitonic transition is significantly reduced compared to spin-coated films. Furthermore, inhomogeneous broadening due to static disorder in the LE peak shows a dramatic reduction from 90 meV to 51 meV, indicating substantially improved crystalline quality.
These spectroscopic differences translate directly into device performance. Under 385 nm UV illumination, bar-coated photodetectors achieve responsivities of 40 mA/W and specific detectivities exceeding 10^(13) Jones at low optical flux, while maintaining ultra-low dark currents below 100 fA. These values place our flexible, solution-processed thin-film devices among the top-performing perovskite UV photodetectors reported to date. In contrast, spin-coated devices operate in a trap-limited regime with responsivities two orders of magnitude lower, directly reflecting the stronger exciton–phonon coupling and higher structural disorder revealed by photoluminescence measurements.
Our results establish that controlling film formation through deposition method selection offers a direct pathway to tune fundamental excitonic properties and drive flexible 2D perovskite films from polycrystalline trap-dominated transport toward quasi-single-crystal-like behavior. This work advances both the fundamental understanding of exciton dynamics in low-dimensional perovskites and the practical development of scalable, flexible radiation detectors for UV sensing applications.