Quantum-dots-based phase separation into a 3D/0D perovskite heterojunction for boosting X-ray detector performance

Direct conversion X-ray detectors based on metal halide perovskites (MHPs), notably CsPbBr₃, promise high performance but suffer from detrimental dark currents and ion migration. Engineering stable and effective electrode interfaces remains a critical bottleneck. This work introduces a quantum dot (QD)-assisted hot-pressing strategy enabling precise control over the interfacial electric field (IEF) through tailored CsPbBr₃/Cs₄PbBr₆ heterojunctions. Synergistic defect engineering of precursor QDs and controlled secondary growth of QD nanocrystals during hot-pressing facilitate the formation of heterostructures with tunable phase composition at the interface. Optimized devices feature a thick (101 μm), large-grained (26 μm) orthorhombic CsPbBr₃ absorber integrated with an underlying hexagonal Cs₄PbBr₆ layer. Kelvin probe force microscopy (KPFM) directly verifies a built-in potential step (∼21 mV) at the interface, establishing an IEF that cooperates with the Type-II band alignment to effectively suppress dark current injection, restrict ion migration, and promote efficient charge separation. Consequently, the engineered detectors demonstrate an outstandingly low dark current density (0.1 nA cm^-2 at 1 V mm^-1). The device exhibits dramatically improved carrier transport with an 8-fold enhancement in average lifetime of the charge carrier (from 1.6 ns to 12 ns), and achieves a high X-ray sensitivity of 12 910 μC Gy_air^-1 cm^-2 (at 85 V mm^-1), yet still maintains its ultra-low dark current baseline. When integrated with a 256 × 256 pixel TFT board, a large area X-ray imaging detector was created, which delivered high resolution and high contrast images for various fine industrial products.