X-ray emission spectroscopy of Cu(In,Ga)(S,Se)(2)-based thin film solar cells: Electronic structure, surface oxidation, and buried interfaces

The electronic and chemical structure of Cu(In,Ga)(S,Se)(2) (CIGSSe) thin f ilm surfaces and of relevant interfaces in CIGSSe-based thin film solar cel ls is investigated with a combination of X-ray emission spectroscopy (XES) and photoelectron spectroscopy. Examples of sulfur L-2,L-3 XES spectra of C dS and CIGSSe are discussed in view of resonant excitation, surface oxidati on, and chemical bonding. The combination of the two techniques proves to b e a powerful tool to identify spectral features correlated to certain chemi cal states or bonds. By monitoring these features in interface formation se quences, chemical and electronic information about buried interfaces can be obtained, which will be discussed in detail for the ZnO/CIGSSe interface. The experimental results provide valuable information on the CIGSSe surface and the ZnO/CIGSSe interface and, in general, demonstrate some of the spec troscopic advantages of X-ray emission spectroscopy.