Multiscale Modeling and Back Contact Design of Bifacial Silicon Heterojunction Solar Cells

A back contact of bifacial silicon heterojunction solar cells was investigated and sensitivity of design studied by means of optical and electrical simulations. With 3-D optical simulations the realistic bifacial silicon heterojunction solar cell with metal fingers at the front and back was simulated. Specular illumination was applied at the front and Lambertian diffuse illumination at the back side. The advanced multiscale approach to combine 3-D optical simulations with 2-D electrical simulations is shown. The complete solar cell was simulated and the results were verified on fabricated test samples. The spacing of back finger contacts was optimized in order to improve the electrical performance of the bifacial silicon heterojunction solar cell with respect to albedo and bulk charge carrier lifetime. Furthermore, an outlook of front finger spacing and the finger width on series resistance is shown, while keeping the ratio of finger width and spacing fixed. The study shows the front finger spacing of 1 mm is the most reasonable spacing. By means of simulations the 24% apparent efficiency of the encapsulated cells with charge carrier lifetime in bulk higher than 7 ms is demonstrated and an outlook for the further optimization is discussed.