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Hybrid functional investigation of theincorporation of sodium and potassium inCuInSe2 and Cu2ZnSnSe4
E. Ghorbani, J. Kiss, H. Mirhosseini, T. Kühne, C. Felser
Subtopic: CdTe, CIS and Related Ternary and Quaternary Thin Film Solar Cells and Modules
Event: 31st European Photovoltaic Solar Energy Conference and Exhibition
Session: 3DV.1.56
1271 - 1273
ISBN: 3-936338-39-6
Paper DOI: 10.4229/EUPVSEC20152015-3DV.1.56
0,00 EUR
Document(s): paper, poster


Based on empirical observations, it is widely accepted that extrinsic sodium and potassium impurities play a major role in the efficiency of solar cells based on CuInSe2 (CISe) and in the structurally similar Cu2ZnSnSe4 (CZTSe) light absorber materials. However, so far there is only little known about the most stable inclusion sites, thermodynamics and kinetics of such Na and K-related defects. To shed more light on the energetics on the effect of Na and K impurities, we have investigated the incorporation of Na and K in CuInSe2 (CISe) and Cu2ZnSnSe4 (CZTSe) via hybrid functional calculations. To achieve a comprehensive overview, we have considered a wide variety of lattice sites as potential defect positions. According to our results, among substitutional positions the Cu-sublattice is the most likely to be occupied by Na and K in CISe and CZTSe. A comparison between tetrahedrally coordinated and octahedrally coordinated interstitial sites reveals that, forming tetrahedrally coordinated Na and K interstitials is energetically more favorable. In both CISe and CZTSe, the formation energy of Na-defects are lower than the formation of K-defects. Thus, if a site is already occupied by Na, than the K introduced into the cell via post-treatment cannot substitute Na easily. Among three possible dumbbells, i.e. (Na-Na), (Na-K) and (K-K) dumbbells, the creation of (Na-Na) dumbbells is energetically the most favorable both in CISe and CZTSe. Formation of VSe-related defects is highly unlikely in CISe and CZTSe.