How Oxygen Exposure Improves the Back Contact and Performance of Antimony Selenide Solar Cells
2020
Fleck, Nicole | Hutter, Oliver S. | Phillips, Laurie J. | Shiel, Huw | Hobson, Theodore D. C. | Dhanak, Vin R. | Veal, Tim D. | Jäckel, Frank | Durose, Ken | Major, Jonathan D.
The improvement of antimony selenide solar cells by short-term air exposure is explained using complementary cell and material studies. We demonstrate that exposure to air yields a relative efficiency improvement of n-type Sb₂Se₃ solar cells of ca. 10% by oxidation of the back surface and a reduction in the back contact barrier height (measured by J–V–T) from 320 to 280 meV. X-ray photoelectron spectroscopy (XPS) measurements of the back surface reveal that during 5 days in air, Sb₂O₃ content at the sample surface increased by 27%, leaving a more Se-rich Sb₂Se₃ film along with a 4% increase in elemental Se. Conversely, exposure to 5 days of vacuum resulted in a loss of Se from the Sb₂Se₃ film, which increased the back contact barrier height to 370 meV. Inclusion of a thermally evaporated thin film of Sb₂O₃ and Se at the back of the Sb₂Se₃ absorber achieved a peak solar cell efficiency of 5.87%. These results demonstrate the importance of a Se-rich back surface for high-efficiency devices and the positive effects of an ultrathin antimony oxide layer. This study reveals a possible role of back contact etching in exposing a beneficial back surface and provides a route to increasing device efficiency.
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