Solvothermal synthesis of mixed-valance Sn2+/Sn4+-SnSe nanoflakes for self-powered photodetectors

<jats:title>Abstract</jats:title>

<jats:p>

In this study, mixed-valence Sn

<jats:sup>2+</jats:sup>

/Sn

<jats:sup>4+</jats:sup>

tin selenide (SnSe/SnSe

<jats:sub>2</jats:sub>

) 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

<jats:sub>2</jats:sub>

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

<jats:sup>−9</jats:sup>

A, indicating suppressed leakage current. Additionally, the rectification ratio increased by approximately two orders of magnitude (∼10

<jats:sup>6</jats:sup>

), 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

<jats:sup>−1</jats:sup>

under UV illumination, while the specific detectivity was on the order of ∼10

<jats:sup>10</jats:sup>

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

<jats:sub>2</jats:sub>

NFs significantly enhances interfacial charge transport and photodetection performance, highlighting their potential for low-power and self-powered optoelectronic applications.

</jats:p>