Electronic and chemical properties of non vacuum deposited chalcopyrite solar cells

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