Exploring Lead-Free Hybrid Double Perovskite Crystals of (BA)₂CsAgBiBr₇ with Large Mobility-Lifetime Product toward X-Ray Detection

Halide double perovskites have recently bloomed as the green candidates for optoelectronic applications, such as X-ray detection. Despite great efforts, the exploration of promising organic–inorganic hybrid double perovskites toward X-ray detection remains unsuccessful. Now, single crystals of the lead-free hybrid double perovskite, (BA)₂CsAgBiBr₇ (BA⁺ is n-butylammonium), featuring the unique 2D multilayered quantum-confined motif, enable quite large μτ (mobility-lifetime) product up to 1.21×10⁻³ cm² V⁻¹. This figure-of-merit realized in 2D hybrid double perovskites is unprecedented and comparable with that of CH₃NH₃PbI₃ wafers. (BA)₂CsAgBiBr₇ crystals also exhibit other intriguing attributes for X-ray detection, including high bulk resistivity, low density of defects and traps, and large X-ray attenuation coefficient. Consequently, a vertical-structure crystal device under X-ray source yields a superior sensitivity of 4.2 μC Gy_air⁻¹ cm⁻².