INVESTIGATION OF THE IN-DEPTH GALLIUM PROFILE IN CO-EVAPORATED Cu(In,Ga)Se_2 THIN FILMS AND ITS INFLUENCE ON PHOTOVOLTAIC APPLICATIONS

摘要

In this work, we describe the influence of two deposition parameters on the material’s in-depth gallium gradient, structural properties and the opto-electronic properties of finished solar cells from these absorbers. We deposited Cu(In,Ga)Se_2 thin films on Mo-coated soda-lime glass substrates using a 3-stage co-evaporation process. Different Ga profiles are obtained by varying the deposition rates of In and Ga in either the first or the third stage. The material’s composition, its crystal structure and phases with different Ga concentrations are investigated by x-ray diffraction. Grazing incidence x-ray diffraction is used to access in-depth variations of the lattice parameter due to different concentration ratios c_(Ga)/(c_(Ga)+c_(In)). Photovoltaic devices are completed with a CdS buffer layer, i-ZnO layer and ZnO:Al front contact and the opto-electronic properties are investigated by current-voltage and spectral quantum efficiency measurements. In conclusion the results from the characterization methods are correlated to the absorber deposition process and diffusion phenomena.