Ultrafast and Highly Responsive Near-Infrared Photodetector Based on PdSe2/Cs3BiSbI9 Type-I Heterojunction.

Two-dimensional (2D) PdSe2 has great application potential for broadband photodetection from the visible to near-infrared spectral region owing to its tunable bandgap, relatively high room-temperature carrier mobility, and excellent air stability. However, PdSe2-based photodetectors typically suffer from relatively high dark current and limited response speed, which hinder their practical applications in weak-light and fast near-infrared detection. In this work, a vertical PdSe2/Cs3BiSbI9 type-I heterojunction photodetector was successfully fabricated by integrating centimeter-scale PdSe2 films grown via self-limited liquid-phase edge epitaxy with air-stable Sb-alloyed lead-free perovskite Cs3BiSbI9. Ultraviolet photoelectron spectroscopy results confirm that both the conduction band and valence band of PdSe2 are located within the bandgap of Cs3BiSbI9, forming a type-I band alignment. In this heterojunction, PdSe2 serves as the main near-infrared absorption and carrier-transport channel, while Cs3BiSbI9 provides interfacial barrier modulation and a built-in electric field induced by Fermi-level equilibration, thereby suppressing dark carrier injection and modifying interfacial carrier dynamics. Under 808 nm laser illumination, the device exhibits a responsivity of 22.2 A W-1, a specific detectivity of 1.64 × 1012 Jones, and a microsecond-level rise time of 52.1 μs. Moreover, the heterojunction detector also retains favorable photodetection performance under 1208 nm laser illumination. Compared with intrinsic PdSe2 and PdSe2 homojunction detectors, the PdSe2/Cs3BiSbI9 heterojunction detector exhibits superior overall performance. These results indicate that type-I interfacial band engineering provides an effective strategy for preparing high-performance PdSe2-based near-infrared photodetectors.