Abstract
M.Sc.
As environmental and energy resource concerns have increased, greater stress has been placed on development of renewable energy resources such as photovoltaic electric generators. CuInSe2/ZnO heterojunction solar cells are currently one of the most promising technologies. 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) production of completed CuInSe2/CdS/ZnO solar cell devices. A new two-stage growth process was developed which involved a low temperature precursor formation step and a subsequent high temperature selenization step. Selenium containing Cu-In-Ga and Cu-In-Ga-Se precursors were deposited by a thermal process in which the constituent elements were evaporated from a single graphite crucible onto heated substrates in presence of a selenium overpressure. These precursors were subsequently reacted in vacuum to elemental selenium 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 300„aC and 600„aC. The structural features (morphology, presence of crystalline phases, bulk and in-depth compositional uniformity) 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.
Prof. V. Alberts