Smooth and Compact All‐Inorganic Perovskite Based Heterojunction Films Enabled by Nanocomposite‐Buffered Thermal Imprint for Highly Sensitive X‐Ray Detection

Abstract Chemical vapor deposition (CVD) is a promising way to fabricate perovskite polycrystalline films for optoelectronic device applications. However, it remains challenging to prepare thick yet smooth and compact all‐inorganic perovskite films by this method, which is of paramount importance for efficient X‐ray detection. In this work, a nanocomposite‐buffered thermal imprint strategy is proposed to improve the surface roughness and eliminate pinholes in CVD‐processed cesium‐lead‐bromide perovskite films with thickness above 40 µm, which is realized by spray‐coating a soft layer composed of organic semiconductors and perovskite quantum dots on top of the perovskite layer and then perform the thermal imprint to prepare the heterojunction films. It is demonstrated that the thermal imprint process can reduce the dark current and noise, enhance the carrier transport properties, as well as improve the spatial uniformity of the devices. Consequently, the optimal detectors show a large sensitivity up to 2 × 10⁴ µC Gy_air⁻¹ cm⁻² and a very low detection limit of 15 nGy_air s⁻¹ that represents one of the most sensitive polycrystalline perovskite X‐ray detectors to date, which highlights the great potential of thermal‐imprinted heterojunction films for realizing high performance X‐ray detection and imaging.