Self-powered dual-heterojunction ZnO/Ag₂Se/Si photodetector with synergistic band alignment for broadband detection from ultraviolet to near-infrared

Broadband photodetectors are critical for multispectral imaging, environmental monitoring, and optical communication. Zinc oxide (ZnO), known for its high electron mobility and excellent stability, is frequently integrated into heterojunctions to achieve broadband photodetection. Nevertheless, such ZnO-based heterostructures commonly encounter performance constraints, including interfacial defect states, lattice mismatch, and impeded carrier transport, which collectively degrade the response speed and spectral efficiency. This work demonstrates a self-powered photodetector based on a monolithic ZnO/Ag₂Se/Si dual-heterojunction fabricated via magnetron sputtering. The complementary band structures and synergistic built-in electric fields at the dual heterointerfaces facilitate efficient carrier separation and collection, enabling a broad detection spectrum from 220 nm to 1550 nm without external power. The device exhibits a responsivity of 1.71 mA/W at 750 nm with a response time of 16.69/17.34 ms (rise/fall). Given its high sensitivity in the near-infrared region, the photodetector successfully decodes 950 nm optical signals into ASCII text, confirming its potential for optical communication. This work provides a feasible strategy for high-performance, self-powered broadband photodetection through rational heterojunction design.