High-Performance Self-Powered PbSe/Ag2Se Heterojunction Photodetector Enabled by Annealing-Induced in Situ Electrode Phase Conversion

Lead selenide (PbSe) thin films are attractive for room-temperature infrared photodetection, yet efficient self-powered operation relies on the construction of a high-quality heterojunction. Herein, an asymmetric Ag/PbSe/Ni electrode structure was fabricated and subsequently annealed in an O2 atmosphere, inducing Ag diffusion into the PbSe film and in situ phase conversion at the Ag/PbSe interface to form Ag2Se. As a result, a high-quality Ag/Ag2Se/PbSe/Ni heterojunction was directly constructed. Under zero bias and 1550 nm illumination, the device exhibits an ultralow dark current of 1.61 × 10-9 A, an Ion/Ioff ratio of 521, detectivity of 7.73 × 1010 Jones, and responsivity of 8.78 mA/W, demonstrating excellent self-powered infrared photodetection performance. Notably, the Ag electrode serves not only as an electrical contact but also as a precursor for heterojunction formation through in situ phase conversion, simplifying device fabrication while simultaneously improving photoresponse performance. First-principles calculations further corroborate that the robust built-in electric field at the heterojunction interface facilitates carrier separation. This work provides a simple and cost-effective strategy for developing high-performance, low-power-consumption self-powered infrared photodetectors.