Johnson, B.; Klaer, J.; Merdes, S.; Gorgoi, M.; Höpfner, B.; Vollmer, A.; Lauermann, I.: Limitations of Near Edge X-Ray Absorption Fine Structure as a tool for observing conduction bands in chalcopyrite solar cell heterojunctions. Journal of Electron Spectroscopy and Related Phenomena 190 (2013), p. 42-46
Open Accesn Version
A non-optimized interface band alignment in a heterojunctionbased solar cell can have negative eff ects on the current and voltage characteristics of the resulting device. To evaluate the use of Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS) as a means to measure the conduction band position, Cu(In,Ga)S2 chalcopyrite thin film surfaces were investigated as these form the absorber layer in solar cells with the structure ZnO/Buffer/Cu(In,Ga)S2/Mo/Glass. The composition dependence of the structure of the conduction bands of CuInxGa1-xS2 has been revealed for x = 0, 0.67 and 1 with both hard and soft NEXAFS and the resulting changes in conduction band off set at the junction with the bu ffer layer discussed. A comprehensive study of the positions of the absorption edges of all elements was carried out and the development of the conduction band with Ga content was observed, also with respect to calculated densities of states.