Yifan Ding, Shuang Liu, Hongyu Tang, Weiqi Shi, Weibo Duan, Qingyuan Cai, Zhiping Zhang, Shaojuan Li, Yuxiang Zheng, Rongjun Zhang
Abstract Despite being key materials for overcoming limitations in traditional optoelectronic technologies, 2D transition metal dichalcogenides (TMDs) still face challenges due to intrinsic defects that hinder carrier transport, making interfacial modulation essential for enhancing photovoltaic performance. In this study, MoSSe/MoSe 2 van der Waals heterojunction photodetectors with type‐II band alignment are constructed through a combined strategy of alloying and heterojunction energy band modulation. The built‐in electric field formed at the heterojunction interface significantly enhances the photoelectric conversion efficiency of the device, achieving an external quantum efficiency ( EQE ) of up to 470% under 550 nm illumination. Under zero bias, the device exhibits excellent self‐powered performance, with an ultra‐low dark current of 5 × 10 −15 A, a high specific detectivity of 2.4 × 10 9 Jones, and an ultra‐broadband spectral response ranging from 200 to 1000 nm. Furthermore, the detector demonstrates considerable potential for applications in cryptographic data transmission and sensitive multi‐wavelength imaging. This work provides new insights into the study of 2D TMDs alloys and the design of high‐performance photodetectors, highlighting their applicability in optical communications, imaging, and sensing.