Epitaxial Growth of Submillimeter-Thick CH3NH3PbBr3 Perovskite Films via Nitrogen-Regulated Solvent Extraction during the Blade-Coating Process for Sensitive Direct X-ray Detection

Abstract

Due to their exceptional responses to X-ray exposure, lead halide perovskites are recognized as ideal candidates for high-spatial-resolution X-ray detectors. However, an effective method to deposit a large-area, submillimeter-thick, dense perovskite film for X-ray detection has been lacking. In this study, a strategy that combines saturated-solution-induced epitaxial growth with a large-area blade-coating process has been developed to produce large-size, submillimeter-thick CH₃NH₃PbBr₃ perovskite films. The successive deposition of a saturated precursor film does not dissolve the underlying perovskite film. Instead, it promotes epitaxial crystal growth by controlling the crystal growth rate over the nucleation rate. The obtained films exhibit a columnar grain structure with fewer pinholes and negligible residual lattice strain. As a result, under an X-ray source with a working voltage of 40 kV, the obtained thick CH₃NH₃PbBr₃ film achieves X-ray sensitivity of up to 1938 μC Gy_air^–1 cm^–2 under −3 V bias, a reduced dark current drift of 1.78 × 10^–4 nA s^–1 V^–1, and a detection limit of 47 nGy_air s^–1 under a −2 V bias; all the above are among the best performances reported for the CH₃NH₃PbBr₃-based X-ray detectors. Using the point-to-point current scanning method, a clear X-ray image could be obtained. This study presents an effective approach for producing thick, dense, and crack-free perovskite films directly on substrates for future X-ray detection applications.