Solution-Processed Heterojunction Photodiodes Based on WSe₂ Nanosheet Networks

Solution-processed photodetectors incorporating liquid-phase-exfoliated transition metal dichalcogenide nanosheets are widely reported. However, previous studies mainly focus on the fabrication of photoconductors, rather than photodiodes which tend to be based on heterojunctions and are harder to fabricate. Especially, there are rare reports on introducing commonly used transport layers into heterojunctions based on nanosheet networks. In this study, a reliable solution-processing method is reported to fabricate heterojunction diodes with tungsten selenide (WSe2) nanosheets as the optical absorbing material and PEDOT: PSS and ZnO as injection/transport-layer materials. By varying the transport layer combinations, the obtained heterojunctions show rectification ratios of up to approximate to 10(4) at +/- 1 V in the dark, without relying on heavily doped silicon substrates. Upon illumination, the heterojunction can be operated in both photoconductor and photodiode modes and displays self-powered behaviors at zero bias.