Band gap temperature-dependence and exciton-like state in copper antimony sulphide, CuSbS2
Journal article, Peer reviewed
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Original versionAPL Materials. 2018, 6 (8) 10.1063/1.5030207
The temperature-dependence of the band gap of the proposed photovoltaic absorber copper antimony sulphide (CuSbS2) has been studied by Fourier-transform infrared spectroscopy. The direct gap rises from 1.608 to 1.694 eV between 300 and 4.2 K. Below 200 K an exciton-like feature develops above the absorption edge at 1.82 eV. First-principles calculations evaluate band structure, band symmetries, and dipole selection rules, suggesting distinctly enhanced absorption for certain excitonic optical transitions. Striking consistency is seen between predicted dielectric and absorption spectra and those determined by ellipsometry, which reveal rapidly strengthening absorption passing 105 cm−1 at 2.2 eV. These results suggest beneficial photovoltaic performance due to strong optical absorption arising from unusually strong electron–hole interactions in polycrystalline CuSbS2 material. In recent years, the leading technologies for thin-film photovoltaics (TFPV) have achieved performance parity with polycrystalline silicon, with both types reaching 21% cell efficiencies.1 The careful selection of excellent optical absorbers, some 100× stronger than silicon,2 combined with deposition processes matured in the display-industry, gives thin-film modules various cost benefits over crystalline silicon and three times better energy payback times.