Ultrafast-Broadband Photodetector with High Responsivity Based on an Interface-Engineered 2D Perovskite/CdSe Type-II Heterojunction

Two-dimensional (2D) Ruddlesden–Popper perovskite phenylethylammonium lead iodide ((PEA) 2 PbI 4 ) possesses potential photoelectronic properties and is considered to be an ideal material for photodetectors. However, single devices commonly suffer from low responsivity, slow response speed, and narrow detection range, which hinder their applications in imaging, communications, and artificial intelligence (AI). In this work, high-quality 2D (PEA) 2 PbI 4 tetragons (TTs) were synthesized via a unique liquid–air interface floating method and integrated with cadmium selenide (CdSe) nanobelts (NBs) to construct a novel hybrid heterojunction photodetector. It confirms that the formation of type-II band alignment at the heterointerface enables efficient interfacial charge transfer. Notably, the (PEA) 2 PbI 4 /CdSe heterojunction hybrid device exhibits exceptional performance under 450 and 682 nm monochromatic illumination: extremely high responsivity ( R ) (2.80 × 10 3 and 6.39 × 10 3 A/W), excellent detectivity ( D *) (4.09 × 10 13 and 9.32 × 10 13 Jones), large external quantum efficiency (EQE) (7.74 × 10 5 % and 1.16 × 10 6 %), and remarkable I on / I off ratio (3.60 × 10 5 and 8.66 × 10 5 ), as well as fast response speeds (rise/decay time: 108/265 μs and 86/196 μs). Furthermore, the hybrid device overcomes the intrinsic bandgap limitation of (PEA) 2 PbI 4, extending its photoresponse to cover nearly the entire visible spectrum and demonstrating reliable imaging capability. This study provides an innovative strategy for developing high-performance photodetectors with significant practical application potential.