In Situ Directional Growth of 2D/3D Perovskite Hetero-Crystals for Highly Sensitive and Stable X-ray Imaging.

The performance of perovskite X-ray detectors is limited by the stability-sensitivity trade-off. Although 2D/3D heterostructures provide a promising route, fabricating single-crystalline interfaces with minimal defects remains challenging. Here, we develop a seed-mediated in situ directional epitaxy strategy to grow large-area, oriented (PEA)2PbBr4/MAPbBr3 heterocrystals (HE-PPB-MPB) with highly sharp interfaces. Soft lattice matching combined with a patterned PDMS stamp guides van der Waals epitaxy of a uniform 2D layer on 3D perovskite, suppressing interfacial defects and random nucleation. The heterocrystals show an ultralow trap density of 3.02 × 109 cm-3 and anisotropic charge transport, achieving a mobility-lifetime product of 8.94 × 10-3 cm2 V-1 and resistivity of 4.58 × 109 Ω cm along [100]. Configured as an asymmetric p-i-n photodiode, the detector attains a high sensitivity of 21,654 μC Gyair-1 cm-2 and an ultralow dark-current drift of 2.28 × 10-4 pA cm-1 s-1 V-1─two orders lower than conventional 3D devices. It also delivers a low detection limit of 26.7 nGyair s-1, withstands 0.408 Gyair without degradation, and enables high-resolution low-dose X-ray imaging. This work establishes a potentially generalized crystal-growth paradigm for advanced radiation sensing.