[en] This study underscores the pivotal role of sodium (Na) supply in optimizing the optoelectronic properties of wide bandgap (~1.6 eV) Cu(In,Ga)S2 (CIGS) thin film absorbers for high efficiency solar cells. Our findings demonstrate that the synergistic use of Na from the glass substrate, in conjunction with in-situ sodium fluoride (NaF) co-evaporation, significantly enhances the structural and optoelectronic properties of the CIGS. CIGS grown under either Na-deficient or excess conditions exhibits inferior microstructural and optoelectronic properties, whereas an optimal Na supply leads to enhanced photovoltaic performance. Optimal Na incorporation minimizes vertical gallium fluctuations and improves the grain size and crystallinity. An absolute 1 sun calibrated photoluminescence (PL) measurement reveals a substantial suppression of bulk defects and a reduction in non-radiative losses, resulting in a high quasi-fermi level splitting (ΔEF) of 1.07 eV, 93 meV higher than in Na-deficient CIGS with the same bandgap. Optimal Na supply further increases excited carrier decay time, as revealed from time-resolved PL, and hole doping density. Cross-sectional hyperspectral cathodoluminescence mapping reveals that optimal Na supply significantly reduces defect density near the surface, thereby effectively translating ΔEF to open-circuit voltage (VOC). As a result, a champion wide bandgap CIGS solar cell with a cadmium-free ZnSnO buffer layer achieved an impressive VOC of 971 meV and an active area power conversion efficiency of 15.7%, highlighting its potential for advancing tandem photovoltaic technologies with stable inorganic top cell.
Disciplines :
Physics
Author, co-author :
Valluvar Oli, Arivazhagan ; Laboratory for Photovoltaics, Department of Physics and Materials Science Research Unit University of Luxembourg Belvaux Luxembourg
KAUR, Kulwinder ; University of Luxembourg > Faculty of Science, Technology and Medicine (FSTM) > Department of Physics and Materials Science (DPHYMS)
GHARABEIKI, Sevan ; University of Luxembourg > Faculty of Science, Technology and Medicine (FSTM) > Department of Physics and Materials Science (DPHYMS)
Hu, Yucheng ; Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Kusch, Gunnar; Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Hultqvist, Adam; Ångström Solar Center, Division of Solar Cell Technology, Department of Materials Science and Engineering Uppsala University Uppsala Sweden
Törndahl, Tobias; Ångström Solar Center, Division of Solar Cell Technology, Department of Materials Science and Engineering Uppsala University Uppsala Sweden
Hempel, Wolfram ; Zentrum für Sonnenenergie‐ und Wasserstoff‐Forschung Baden‐Württemberg (ZSW) Stuttgart Germany
Witte, Wolfram ; Zentrum für Sonnenenergie‐ und Wasserstoff‐Forschung Baden‐Württemberg (ZSW) Stuttgart Germany
Oliver, Rachel A.; Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
SIEBENTRITT, Susanne ; University of Luxembourg > Faculty of Science, Technology and Medicine (FSTM) > Department of Physics and Materials Science (DPHYMS)
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