Enhanced optical responsivity in photothermoelectric effect of SnSe-SnSe2 composite at near-infrared band

We experimentally demonstrated that composites, being effective in optimizing the thermoelectric performance, can also enhance photothermoelectric effects in this work. In detail, we employed an alternating-growth in chemical-vapor-transport to grow the SnSe-SnSe2 composite crystals. The photo-responsivities of SnSe-SnSe2 (atomic-weight-ratio as 44%-56%) composite are comparable to SnSe crystals in the visible band (444 and 532 nm). However, the responsivities of SnSe-SnSe2 have remarkable 27.3% enhancement than those of SnSe crystal at the near-infrared band (1310 and 1550 nm). Supported by optical spectroscopy and theoretical electronic band structure, the enhanced optical responsivity of SnSe-SnSe2 composites is due to the formation of P-N junctions at interfaces between SnSe and SnSe2, leading to more optical transition channels and corresponding optical absorptions in near-infrared band. Our work verifies that hetero-junction formed among constituent compounds in composites is effective in optimizing the photothermoelectric response of thermoelectric materials in certain electromagnetic bands, paving the way to develop photoelectric detection devices.