Preparation And Characterization Of CIGS Thin Films By Co-Evaporation Process

With the development of human society, people tend to pay more attention to the clean,effective and inexaustibled energy. Solar energy, as a green,harmless and renewable energy, has great advantages and distinct potentials. Solar cells which can solve the energy-dearth and environment-pollution problems at the same time is the main direction of the future utilization of solar energy. Among all the solar cells, CIGS cell is very prominent, it has a multi-crystallinity and a direct band gap, and the highest convertion efficiency about 19.9% of CIGS cells have been produced using the three-stage co-evaporation method, which is also the highest among all the thin film solar cells.CIGS thin films, as the absorption layer and the core part of CIGS solar cell, has became a focus for researchers since 1970's because of its complex composition and difficult controlling conditions.CIGS thin films were mostly deposited by three stage co-evaporation method at room temperature, and then were annealed in vacuum at different temperatures by each step in the paper. The microstructures,surface morphology and optical propeties were characterized by X-ray Diffraction(XRD),Scanning Electron Microscopy(SEM),Energy Dispersive Spectroscopy(EDS) and Ultraviolet Spectrophotometer (UV), respectively. The effects of annealing temperature, Se contents and gas environment condition on the structural and optical properties are also well discussed. The results show that:(1) precuror annealing temperature should reach to 350℃in the three stage co-evaporation, so that In and Ga can be effectively response with Se. (2) Se contents must exactly be within the scope of CuIno.7Ga0.3Se2 stoichiometric, which is conducive to the preparation of CIGS thin films with high absorption rate and low near-infrared optical reflectivity less than 2%. (3) As the annealing temperature of precursor increased, the CIGS thin-film crystal particles are becoming smaller. Annealing temperatures lower than 400℃are valuable to the crystallization of CIGS thin films, while agglomeration phenomenon appears when the temperatures are above 400℃. (4) Within the scope of CuIno.7Gao.3Se2 stoichiometric, the precuror annealing temperature should choose to be 350℃when Se content is normal and 400℃when Se is excessive. And this is conducive to the preparation of CIGS films in a chalcopyrite single-phase. In addition, GIGS thin film was also deposited by one stage co-evaporation method at room temperature in this paper, and its composition, crystalline structure, optical properties were analyzed in order to explore the one-step preparation method of CIGS thin films.