Type-II GaSe/MoS₂ van der Waals Heterojunction for High-Performance Flexible Photodetector

In recent years, two-dimensional (2D) type-II van der Waals (vdW) heterojunctions have emerged as promising candidates for high-performance photodetectors. However, direct experimental evidence confirming the enhancement of photoelectric properties by the heterojunction's type and structure remains scarce. In this work, we present flexible photodetectors based on individual GaSe and MoS2, as well as a vertically stacked type-II GaSe/MoS2 vdW heterojunction on polyethylene terephthalate (PET) substrate. These devices demonstrate outstanding responsivities and rapid response speeds, ensuring stable and repeatable light detection. It is notable that the GaSe/MoS2 heterojunction photodetector exhibits the highest on-off ratio and fastest response speed, attributed to the formation of type-II band alignment. Furthermore, the GaSe/MoS2 heterojunction photodetector maintains robust stability even in a bent state, highlighting remarkable flexibility. This work exemplifies the type-II vdW heterojunctions in enhancing photoelectric properties through direct in-situ experimentation, laying the groundwork for practical applications of 2D flexible photodetectors.