SOLAR-CELLS BASED ON CUINSE2 AND RELATED-COMPOUNDS - MATERIAL AND DEVICE PROPERTIES AND PROCESSING

This paper summarizes recent material and device results obtained at t he Institute of physical Electronics at Sfrcttgart University (IPE). p roperties of the material system Cu(In, Ga)(S, Se)(2) were analysed,se d and wherever possible a correlation between the material properties and the device characteristics is made. Different high-vacuum techniqu es of absorber preparation ave presented and compared The formation of different alloys of the family Cu(In, Ga)(S, Se)(2) is possible for t he co-evaporation and at least one of the sequential evaporation techn iques. The model for Cu-rich growth of CuInSe2, known from the co-evap oration process can also be used for the Cu-rich growth in the sequent ial evaporation processes. The surface composition of slightly (In, Ga )-rich bulk compositions is always determined to be the defect chalcop yrite Cu(In, Ga)(3)Se-5. Solar cells prepared with different processes and therefore different morphologies yielded similar device performan ce. An exponential decay of the density of states from the valence and conduction bands was obtained. Improved cell performance is achieved using absorber layers with higher carrier concentrations. The carrier concentration can be increased by using Na-containing substrates or by utilizing a new Cd-free buffer layer. Device efficiencies in the rang e of 15% were achieved using the Cd-free buffer layer.