Preparation And Characterization Of Absorption Layer In CIGS Thin-film Solar Cells

From last century, solar cells, as a kind of photoelectric conversion devices that has got the attention of researchers. CIGS thin film solar cells have the advance of long life time, high efficiency and low cost, and is becoming a new generation of photoelectric conversion devices substitute for silicon solar cells. The world record efficiency of CIGS thin film solar cells prepared by co-evaporation has exceeded20%. Buy the co-evaporation method have many disadvantages, like, complex equipment, difficult to control source temperature and non-uniform thickness of film. So this method is not suitable for preparing large scale and low cost solar cells. However the sputtering method can solve all these problems.For these reasons, in this paper, we focused our attention on the growth conditions of CIGS thin films prepared by sputtering. We investigated their characters including structure and morphology, and analyzed the effects of growing conditions on the characters of both CIGS thin films and CIGS solar cells.The main contents and results are listed below:1. Investigated effects of precursors’deposition method and selenization temperature on the characters of thin films prepared by sputtering and post selenization method. We optimized the morphology of precursors by changing the deposition method of indium layer. By observing the SEM pictures of thin films, we found that the optimum condition of selenization is at500℃for120minutes. CIGS thin films prepared by this method have smooth surface and its crystalline grains grow along the preferred (112) orientation.2. Investigated effects of growing temperature on the characters of thin films prepared by sputtering single CIGS target. We found that substrate temperature has obviously influences on the character of thin films. The grain size of thin films would be very little when substrate temperature is low and phase separation would appear when substrate temperature is too high. The optimum temperature is between500℃and525℃.3. Investigated a new method of preparing CIGS thin films by evaporating Cu2Se, In2Se3, Ga2Se3mixed powder. We compared morphology and grains orientation of CIGS thin films prepared on different substrates and at different substrate temperatures. We also analyzed the effects of annealing on grain size and electric parameters. The superiority of this method was found by analyzing IV curves of CIGS solar cells.4. Investigated effects of Gallium ratio on the characters of CIGS thin films by using the First-principle method. We verified that the band gap of CIGS will increase with the growth of Gallium ratio and explained its reasons. We also find that the absorption peak of CIGS will shift right if the ratio of Gallium increases.