Electrodeposition Of CuInSe₂ And Cu (In, Ga) Se₂ Thin Films For Solar Cells

The crisis of energy and entironment promote the development of renewable energy worldwide. Comparing to other renewable resources of energy, the solar enery which is clean, safe and abundant, shows the unprecedented advantages. As the most rapidly developing field of solar energy, photovoltaic generation attracts tremendous attenttion and becomes the predominant trend in the utilization of renewable energy. CuInSe2 (CIS) and Cu(In,Ga)Se2 (CIGS) have been the research hotspots in the field of solar cells in the recent years, due to their large optical absorption coefficient, direct band-gap within the maximum solar absorption region, high efficiency and good stabilization. Currently, the electrodeposition of CIS and CIGS has been considered to be a promising approach from the viewpoint of low-cost, high-efficiency, non-vacuum, successive and large area production. The industrialization of CIS and CIGS solar cells based on electrodeposition is expected in the recent future.The electrodeposition of CIS and CIGS thin films are facing two main problems:one is that the stoichiometric composition of films are rather difficult to be controlled, the other one is that the electrodeposition mechanism is unclear. I n this work, aiming to solve these two problems, the following research works are taking:(1) The electrochemical behaviors of CuInSe2 and Cu(In,Ga)Se2 are studied systematically, and the electrodeposition mechanism is analyzed. The results reveal that Se and Cu are first reduced to from the copper selenides. The insertion of In involves three different routes:firstly, surface-induced reduction by copper selenides to form CuInSe2; secondly, reaction with H2Se to form indium selenide; thirdly, the direct reduction of In3+ to In. While the Gallium incorporates through two paths:Ga3+ reacts with H2Se to form gallium selenide; and Ga2O3 forms via Ga3+ hydrolysis from the increase of local pH. (2) Sodium sulfamate has been chosen as the new complexig agent for the acidic solution of CIS and CIGS, whose effects on the electrodeposition progress has been studied. It is found that sodium sulfamate can form complexes with Cu2+ and Cu+, and inhibit the reduction of H2Se03, therefore hinder the formation of copper selenides by reducing their reductive rate. With suitable concentration of sodium sulfamate, the composition and morphology of films can be controlled.(3) The main parameters of electrodeposition process (electrodeposition potential, reagents concentration, deposition temperature and pH) are optimized through investigating the effects of each parameter on the composition and morphology of CIS and CIGS films deposited. The electrodeposition potential, CuCl2 and SeO2 concentration markedly affects the composition and morphology of CIS and CIGS films. While InCl3 and GaCl3 concentrations just affect the deposited In and Ga levels of films. High deposition temperature is not conducive to the reduction of Cu and Se but facilitates the deposition of In and Ga. And the pH has some influence on the composition and morphology of films by affecting the reduction of Se.