A fast-response self-powered UV–Vis–NIR broadband photodetector based on a AgIn₅Se₈/t-Se heterojunction

A type II p–n heterojunction could improve the photodetection performance of a photodetector due to the excellent ability of carrier separation. N-type AgIn₅Se₈ (AIS) exhibits a large optical absorption coefficient, high optical conductivity and a suitable bandgap, and shows potential application in broadband photodetection. Even though our previous study on AgIn₅Se₈/FePSe₃ obtained a good response speed, it still gave low responsivity due to the poor quality of the p-type FePSe₃ thin film. Se, with a direct bandgap (around 1.7 eV), p-type conductivity, high electron mobility and high carrier density, is likely to form a low-dimensional structure, which leads to an increase in the effective contact area of the heterojunction and further improves the photodetector performance. In this work, continuous and dense t-Se thin film was prepared by electrochemical deposition. The self-powered AgIn₅Se₈/t-Se heterojunction photodetector exhibited a broadband detection range from 365 nm to 1200 nm. The responsivity and detectivity of the heterojunction photodetector were 32 μA/W and 1.8 × 10⁹ Jones, respectively, which are around 9 and 4 times higher than those of the AgIn₅Se₈/FePSe₃ heterojunction photodetector. The main reason for this is the good quality of the t-Se thin film and the formation of the low-dimensional t-Se nanoribbons, which optimized the transport pathway of carriers. The results indicate that the AgIn₅Se₈/t-Se heterojunction is an excellent candidate for broadband and self-powered photoelectronic devices.