Solvothermal synthesis of mixed-valance Sn 2+ /Sn 4+ –SnSe nanoflakes for self-powered photodetectors

In this study, mixed-valence Sn 2+ /Sn 4+ tin selenide (SnSe/SnSe 2 ) nanoflakes (NFs) were successfully synthesized via a solvothermal method and employed as an interfacial layer in an Au/SnSe/n–Si/Al heterojunction device. Structural and compositional analyses confirmed the coexistence of SnSe and SnSe 2 phases, while optical measurements revealed strong absorption across the visible–near-infrared region, with direct and indirect band gaps estimated to be 1.62 and 0.98 eV, respectively. The fabricated SnSe/n-Si device exhibited improved electrical characteristics compared to the reference Au/n–Si/Al device, with an ideality factor ranging from 1.53 to 1.62 and a barrier height of 0.80–0.82 eV. The reverse saturation current was reduced to the order of ∼10 −9 A, indicating suppressed leakage current. Additionally, the rectification ratio increased by approximately two orders of magnitude (∼10 6 ), demonstrating enhanced junction quality. Under illumination, the device showed a pronounced photoresponse, particularly in the reverse-bias region, while maintaining stable forward-bias characteristics. A maximum ON/OFF ratio of 6620 (1 Sun) and 1724 (UV, 395 nm) was achieved at −0.5 V. The responsivity reached 0.063 AW −1 under UV illumination, while the specific detectivity was on the order of ∼10 10 Jones. Furthermore, the device exhibited an external quantum efficiency of ∼19% with stable performance across varying bias conditions. These results demonstrate that the incorporation of solvothermally synthesized mixed-valence SnSe/SnSe 2 NFs significantly enhances interfacial charge transport and photodetection performance, highlighting their potential for low-power and self-powered optoelectronic applications.