Cs₂AgBiBr₆ Double Perovskite Single Crystal/ CsPbBr₃ Perovskite Nanocrystals Heterojunction for High‐Performance X‐Ray Detection

Abstract In this study, the investigation of a Cs 2 AgBiBr 6 single crystal (SC) / CsPbBr 3 nanocrystals (NCs) film double perovskite/perovskite type‐II novel heterojunction tailored for superior X‐ray detection applications is presented. One of the main benefits of utilizing such a heterojunction is its built‐in electric potential, which improves charge transport and reduces the dark current in the devices. By casting CsPbBr 3 NCs onto polished Cs 2 AgBiBr 6 SC, the Cs 2 AgBiBr 6 /CsPbBr 3 double perovskite/ perovskite heterojunction is fabricated. The heterojunction X‐ray detector exhibits reduced dark current and increased photocurrent compared to the pristine SC device. This enhancement of photocurrent can be attributed to efficient carrier generation and separation facilitated by appropriate band bending at the type‐II heterojunction interface. The heterojunction device shows an X‐ray sensitivity of 6 µCGy −1 cm −2 at 0 V of applied bias, owing to the built‐in potential across the heterojunction. Remarkably, at a −50 V bias, the sensitivity of the heterojunction device reached 857.8 µCGy −1 cm −2 , with a limit of detection of 312 nGy s −1 . Density functional theory (DFT) calculations provided further insights, revealing electron transfer from CsPbBr 3 to Cs 2 AgBiBr 6 , thereby enhancing the X‐ray sensitivity of the heterojunction device. These findings underscore the potential of Cs 2 AgBiBr 6 /CsPbBr 3 heterojunctions for X‐ray detection and optoelectronic applications.