3D simulations for the optimization of antireflection subwavelength structures in CIGS solar cells

A three-dimensional simulation study was carried out for the optimum design of subwavelength structures (SWSs) on a CuIn_1-xGa_xSe₂ (CIGS) solar cell regarding the antireflection properties. Numerical calculations were implemented for various shapes of SWSs with conic, parabolic, quadratic cross-sectional profiles, along with diverse CIGS composition ratios of x=0.2, 0.4, and 0.75. The reflectance was obtained successfully for individual configuration sets with subsequent computations of the effective reflectance. The simulated reflectance was found to be strongly dependent on the aspect ratio of the SWS, whereas it was highly insensitive to the thickness of the ZnO layer. The effective reflectance drops to approximately 5% and below 2% when the aspect ratio is 1 and 2, respectively. The simulation result indicates that a cone-shaped SWS enhances the transmittance more effectively than parabolic and quadratic SWSs. The reflectance of the optimized SWS was also compared to that of a CIGS solar cell with conventional MgF₂ antireflection coatings (ARCs). Multi-layer SWSs tend to be the most efficient surface structure with broadband and wide-angle antireflection.