Preparation And Characterization Of CuInSe₂ And Cu(In, Ga)Se₂ Thin Films By Electrodeposition

For the sake of environmental protection and energy conservation, the search for renewable, cheap and clean energy source has been an essential problem for humankind. Among these solar energy is a kind of new energy with clear, safe, no pollution, no effect on environment and reproducible. At present, thin film solar cells are the most interesting project in the realm of solar cells research and development. CuInSe2 (CIS) is a highly promising semiconductor material for thin film solar cells, which possesses optimum energy band gap and extraordinarily high absorption coefficient and long-term stability without any signs of degradation, high photoelectric conversion efficiency, and low-cost and environmental protection. But CIS possesses band gap energy equal to 1.04eV, which is not within the maximum solar absorption region. The addition of gallium to CIS to form CIGS can increase the band gap from 1.04eV to 1.6eV that can potentially achieve high conversion efficiency in CIGS thin film solar cells.CIS and CIGS thin films materials for solar cells were fabricated by potentiostatic electrodeposition on Mo thin films/soda-lime glass (SLG), where the reference electrode was a saturated calomel electrode (SCE), the counter electrode was Pt gauze and the working electrode was a Mo/SLG substrate. The solution is consisted of copper chloride, indium chloride, gallium chloride, selenious acid and Na- citrate. CIS and CIGS thin films were annealed for a short time to improve the stoichiometry. The selenized films were characterized by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) etc.At first Mo thin films substrate were prepared by magnetron sputtering on the SLG. The results indicate Mo thin films have low-resistivity on SLG substrates with good adhesion, smooth surface and compact grains, which accord with the ohmic contact of solar cells.Then the factors, which influence the electrodeposition, were analyzed and discussed. CIS thin films that have chalcopyrite structure were successfully prepared by electrodeposition. The crystallinity was improved after heat-treatment in seleniumpowder atmosphere. The type of conduction depends on the ratio of Cu/In. The films is p-type when the ratio is greater than 1, on the contrary the films is n-type. The absorption coefficient of the films reaches 4.3×104cm-1 and the band-gap is between 1.04eV and 1.14eV.Finally the process of CIGS thin films by electrodeposition is discussed. The results show that CIGS thin films by electrodeposition have chalcopyrite and polycrystalline structure. CIGS thin films have better crystallinity with the increase in Na-citrate's concentration and heat treatment temperature. The type of conduction depends on the ratio of Cu/(In+Ga). The films is p-type when the ratio is greater than 1, on the contrary the films is n-type. The absorption coefficient of the films reaches 4.6×104cm-1 and the band-gap is between 1.43eV and 1.50eV.