Horsley, K.; Pookpanratana, S.; Krause, S.; Hofmann, T.; Blum, M.; Weinhardt, L.; Bär, M.; George, K.; Van Duren, J.; Jackrel, D.; Heske, C.: Electronic and chemical properties of non-vacuum deposited chalcopyrite solar cells. In: IEEE [Ed.] : 37th IEEE Photovoltaic Specialists Conference, Washington, June 19-24, 2011Piscataway, NJ, 2011. - ISBN 978-1-4244-9965-6, p. 000374-000378
Abstract:
We have investigated the electronic and chemical surface properties of a Cu(In1-xGax)Se2 (CIGSe) thin-film solar cell absorber and a CdS/CIGSe interface sample taken from Nanosolar’s manufacturing line. Using soft x-ray and UV photoelectron spectroscopy, inverse photoemission, and x-ray emission spectroscopy employing high-brilliance synchrotron radiation, we have determined the chemical composition of the surface and near-surface bulk, as well as some of the relevant electronic structure parameters (e.g., the surface band gap of the absorber). We find that the (previously air-exposed) surfaces show a surprisingly low degree of carbon-containing surface adsorbates, the presence of sodium and selenium oxide species on the surface of both samples, a significant S/Se intermixing at the CdS/CIGSe interface, and, as is common for high-efficiency CIGSe absorbers after surface cleaning, an electronic surface band gap (1.45 ± 0.15 eV) that is noticeably larger than the optical bulk band gap.