Performance Limits and Status of Single-Junction Solar Cells With Emphasis on CIGS

Limitations in performance and the status of single-junction solar cells are reviewed. Conversion efficiency in single-junction solar cells is systematically analyzed in terms of energy conversion efficiency, the Shockley-Queisser (SQ) efficiency limit, and two remaining efficiencies, i.e., optical efficiency and electrical efficiency normalized to the SQ limit of performance parameters. There is a weak dependence of the SQ efficiency limit in single-junction solar cells on the bandgap of the absorber and much stronger dependence of the electrical efficiency. In the case of Cu(In,Ga)(Se,S)₂ (CIGS) solar cells, the bandgap can be varied through In/Ga and/or Se/S content from 1.04 to 1.7 eV, which allows considerable opportunity to optimize the bandgap. Although the record CIGS cells have a bandgap below 1.2 eV, the SQ efficiency limit predicts slightly higher efficiencies for bandgaps near 1.34 eV.