Otimização e desenvolvimento de células solares industriais em substratos de silício multicristalino

摘要

The exponential growth of the photovoltaic devices market and the necessity of material with low cost make the multicrystalline silicon an important option for solar cell industry. The goal of this thesis is to optimize and develop the main processes for manufacturing multicrystalline silicon solar cells, with the structure n+pn+ and 36 cm2 of area. The highly doped regions and the metal grids were optimized by simulations and the emitter and the firing conditions of the metal pastes for screen printing metallization were optimized experimentally. According to the obtained results from the optimization by simulations, it is possible to obtain solar cells with 16,2 % of efficiency for high values of the minority carriers lifetime of 100 μs and with back surface field. The efficiency of 15,8 %, 14,6 % and 12,1 % can be obtained for lower lifetimes of 50 μs, 10 μs e 1 μs, respectively, with screen printing metallization and metal grid with fingers of 100 μm width. The efficiency was reduced of around 0,3 % to 0,5 %, when the width of the grid fingers are increased from 100 μm to 200 μm. It was also verified that as larger are the fingers width, larger is the depth of the junction and the back surface field for the same surface concentration. In the process for the experimental optimization of the emitter, the sheet resistance was obtained according to the diffusion temperature. The temperature and the time to obtain the sheet resistance of 50 Ω/□, selected for the manufacturing of solar cells with metallization through screen printing, is 820 ºC and 30 minutes. From the analysis of manufactured solar cells, we verified that the temperature of the pastes firing affects the solar cells performance, while the belt speed almost does not influence on the cell electrical parameters. Higher efficiencies were found for the temperature of the firing between 860 oC and 880 oC. We also observed that the thickness of the antireflecting coating influences the fill factor and the current of the solar cells. The highest efficiency achieved was 11,5 %, with fill factor of 0,74, for the firing temperature of 860 ºC, belt speed of 190 cm/min and double antireflecting layer of Si3N4 e TiO2.