Abstract
M.Sc.
I-III-VI2 compound semiconductors are important photovoltaic (PV) materials with optical and electrical properties that can be tuned for optimum device performance. Recent studies indicated that the efficiencies (1) > 18%) of CuInSe2/CdS/ZnO thin film devices are in good agreement with that of standard silicon cells. In this study, CuInSe 2 absorber films with excellent material properties were produced by relatively simple and reproducible two-stage growth techniques. In these approaches, metallic precursors (Cu/InSe, InSe/Cu, Cu/InSe/Cu and InSe/Cu/InSe) were deposited by thermal evaporation from specially designed graphite heaters at temperatures around 200°C. In the second stage of the process, the alloys were exposed to elemental Se vapour or H2Se/Ar gas. A systematic study was conducted in order to determine optimum growth parameters for the different deposition processes. Optimum material properties (homogeneous and dense films with a high degree of compositional uniformity) were obtained when InSe/Cu/InSe precursors were selenized in elemental Se vapour or H2Se/Ar gas. Comparative studies also indicated that the reaction kinetics is enhanced when H2Se/Ar is used as chalcogen source. Fully selenized films were obtained at temperatures as low as 450°C in a H2Se/Ar atmosphere, compared to temperatures of 600°C in the case of Se vapour. The optical and electrical properties of the absorber layers were accurately controlled by small variations in the bulk composition of the films. A standard CdS/ZnO window layer technology was also developed in our laboratories and preliminary solar cell devices were fabricated and evaluated.