Keywords :
composition; Cu(In,Ga)S2; CuGaS2; CuGaS2 solar cell; electronic defect; photoluminescence; quasi-Fermi level splitting; tandem; Composition dependence; Cu(in,ga)S2; Deep-levels; Electronic defects; Level transition; Photovoltaics; Quasi-Fermi level splitting; Research and application; Tandem; Electronic, Optical and Magnetic Materials; Renewable Energy, Sustainability and the Environment; Condensed Matter Physics; Electrical and Electronic Engineering
Abstract :
[en] CuGaS2 films grown by physical vapor deposition were studied by photoluminescence (PL) spectroscopy, using excitation intensity and temperature-dependent analyses. We observed free and bound exciton recombinations, three donor-to-acceptor (DA) transitions, and deep-level transitions. The DA transitions at ~2.41, 2.398, and ~2.29 eV are attributed to a common donor level ~35 meV and two shallow acceptors at ~75 and ~90 meV and a deeper acceptor at 210 meV above the valence band. This electronic structure is similar to those of other chalcopyrite materials. The observed DA transitions are accompanied by several phonon replicas. The Cu-rich and near-stoichiometric CuGaS2 films are dominated by transitions involving the acceptor at 210 meV. All films show deep-level transitions at ~2.15 and 1.85 eV due to broad deep defect bands. The slightly Cu-deficient films were dominated by intense transitions at ~2.45 eV, which were attributed to excitonic transitions, and a broad defect transition at 2.15 eV.
Funding text :
The authors acknowledge that this research was funded in whole, or in part, by the Luxembourg National Research Fund (FNR), in the framework of the MASSENA project (Grant PRIDE 15/10935404). For the purpose of open access, the author has applied for a Creative Commons Attributions 4.0 International (CC BY 4.0) license to any Author Accepted Manuscript version arising from this submission. We also acknowledge Dr. Mael Guennou for the Raman spectroscopy of the CuGaS film. 2
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