Development and Fabrication of Thin-Film CIGS Solar Cells with Multilayer Anti-Reflection Coatings / Diffraction Gratings (II)

Recently, Cu(In,Ga)Se2 (CIGS) compound semiconductors have attracted a lot of attention on the realization of cost-effective solar energy systems due to their unique properties including high conversion efficiency, low production costs, a wide absorption range, highly flexible of light intensity and incident angle, long-term reliability, and feasibility of a large-area cell, etc. Therefore, the objective of this project is focused on development and fabrication of CIGS solar cells with improved performances. The conventional structure of CIGS solar cell is composed of anti-reflection layer, transparent conduction oxide, thin film buffer layer, light absorption layer, and the back-contact electrode. In the first-year, the program is started with deposition of molybdenum (Mo)/indium tin oxide (ITO) electrodes on soda-lime glass by the traditional sputtering system, and then using electrodeposition in combination with the selenized process to synthesize CIGS with well-controlled compositions. In order to obtain a good heterojunction characteristic and to reduce the probability of carrier recombination, a wide-bandgap CdS (Eg = 2.26 ~ 2.5 eV) is directly deposited on CIGS by chemical bath deposition (CBD). Further, the transparent conduction oxides with a high transmittance and a low contact resistance will be used as the window layer. In this project, aluminum-doped zinc oxide (ZnO:Al) fabricated by sputter deposition could meet our demands. In contrast to the use of single-layer MgF2 as an anti-reflection layer, the effect of Fresnel reflection could be further suppressed by multilayer anti-reflection coating and thus the conversion efficiency of solar cells can be enhanced apparently. In addition, surface texturing can be integrated into the solar cells to achieve the same results. To date, researches associated with the integration of periodic diffraction gratings on Si solar cells have been extensively studied. Consequently, diffraction optical elements (DOE) have shown the ability to improve the device performance significantly. However, there is almost no the report based upon the influence of utilizing the DOE on CIGS solar cell. In the second year, we will fabricate the DOE on the top of CIGS solar cells to increase the amount of trapped lights and to suppress the outgoing zero-order wave as well. Experimentally, the diffraction grating with a given geometry will be designed carefully by using FDTD software, and then the one-dimensional or two-dimensional periodic gratings are performed by holography or electron-beam lithography. It is expected that the quantum efficiency of solar cells with the DOE could be improved as compared to the device without it.

Project ID:PB10001-1178
External Project ID:NSC100-2623-E182-004-ET