In Situ Epitaxial Growth of Centimeter-Sized Lead-Free (BA)2CsAgBiBr7/Cs2AgBiBr6 Heterocrystals for Self-Driven X-ray Detection.

Halide perovskite heterocrystals, composed of distinct perovskite single crystals, have generated great interest for both fundamental research and applied device designs. One of the key advantages of using such a heterocrystal is its built-in electric potential, which enhances charge transport and suppresses the noise in the solid-state devices. On the basis of this strategy, high-performance optoelectronic devices (e.g., X-ray detectors) have been successfully demonstrated. However, the toxicity of metal cations (Pb) in those reported heterocrystals hinders their wider applications. Thus, developing lead-free halide perovskite heterocrystals is significant but remains highly challenging. Here, we report a solution-processed in situ heteroepitaxial approach that enables us to create the first lead-free halide perovskite heterocrystal, (BA)2CsAgBiBr7/Cs2AgBiBr6(BA = n-butylammonium), with dimensions of up to 10 × 7 × 6 mm3. The as-grown heterocrystals have high crystalline quality and present near atomically sharp interfaces. More excitingly, the (BA)2CsAgBiBr7/Cs2AgBiBr6 heterogeneous integration allows the formation of a built-in electric potential in the junction, which triggers spontaneous charge separation/transport. Consequently, X-ray detectors using the heterocrystals can operate in a self-driven mode and exhibit an impressive sensitivity (206 μC Gy-1 cm-2) superior to that of the pristine Cs2AgBiBr6 crystal detectors, an ultralow dark current, and operational stability. Our findings provide the first demonstration of lead-free halide perovskite heterocrystals and may open up opportunities for a host of sustainable and miniaturized perovskite optoelectronic devices.