Abstract
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.
Highlights
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]
Gallium, and indium are relatively expensive,[4] indium and tellurium () are scarce with limited geographical availability,[5] and concerns remain over cadmium toxicity.[6,7,8,9]
P-type, due to shallow acceptor-like V Cu and V S vacancies and anti-site CuSb defects,[17,19] carrier concentration is tunable from 1016 to 1018 cm−3 through growth parameters.[6]. These defect states are occupied at 300 K, blocking recombination via these centers and permitting conduction-band minimum to valenceband maximum radiative-recombination: rather unusual in indirect semiconductors as non-radiative recombination usually dominates.[19]
Summary
The leading technologies for thin-film photovoltaics (TFPV) have achieved performance parity with polycrystalline silicon, with both types reaching 21% cell efficiencies.[1].
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