Columnar Grain Growth of Lead-Free Double Perovskite Using Mist Deposition Method for Sensitive X-ray Detectors

Abstract

The sensitivity of X-ray detectors can be effectively improved by forming a columnar grain structure in the photoconductive layer, given that few grain boundaries exist across the direction of electron–hole pair collection. Herein, we demonstrate the fabrication of Cs₂AgBiBr₆ films with columnar grain structures using the mist deposition method. An X-ray detector based on a 92 μm-thick Cs₂AgBiBr₆ film with columnar grains exhibits a high sensitivity of 487 μC Gyair⁻¹ cm⁻², which is the highest among detectors based on Cs₂AgBiBr₆ polycrystalline thick films. To reveal the mechanism of columnar grain growth, we investigate the effects of deposition conditions, including the precursor solution concentration and substrate temperature. From the results, we conclude that the re-dissolution capability of the precursor solution is a key factor promoting the grain growth on the film surface, leading to columnar growth. Furthermore, we realize the columnar grain growth of a CH3NH3PbBr3 film to demonstrate the generality of the mist deposition method.