Optimization of the structural properties of selenized metallic alloys

M.Sc.CuInSe2/CdS/ZnO heterojunction solar cells are currently one of the most promising technologies for the production of economically viable energy in the form of electricity. The key component of this thin film solar cell device is the chalcopyrite absorber film. CuInSe2 and its related alloys such as Cu(In,Ga)Se2 have been deposited by a number of techniques, including methods which have been demonstrated to be scalable to mass production volumes. In this study attention was focused on (i) developing a relatively simple deposition technology for the production of chalcopyrite absorber films, (ii) detailed characterization of the semiconductor thin films in terms of the experimental parameters and (iii) fabrication of completed CuInSe2/CdS/ZnO solar cell devices. Metallic precursors comprising of copper and indium were deposited with electron-beam evaporation. The number of elemental layers in the precursor stack as well as the substrate temperature was optimized in order to produce metallic alloys with optimum structural properties. These precursors were subsequently reacted in vacuum to elemental Se vapour or to H2Se/Ar at atmospheric pressure in a separate diffusion reactor. In order to investigate the growth kinetics of the respective processes, the precursors were reacted to the Se in the temperature range between 350°C and 450°C. The structural features (morphology, presence of crystalline phases and bulk compositional properties) of the respective films were compared and correlated against the growth parameters. From this systematic study, optimum growth parameters were determined for the production of completed solar cell devices.Professor V. Albert