Texturing of the back reflector for light trapping enhancement in micromorph thin film solar cells

The effects of textured back reflectors on light trapping in a-Si:H/μc-Si:H tandem cells are investigated with textured ZnO:Ga (GZO) back contacts obtained by surface wet etching. It is observed that rough back reflectors in fabricated tandem solar cells increase the short circuit current density of the bottom cells by 8%, which is attributed to light-trapping improvement. It is shown that enhanced longer wavelength light trapping is mainly attributable to improved light scattering at the back side by comparing identical a-Si:H/μc-Si:H tandem solar cells, both with a GZO back reflector but only one with a textured back reflector. The effectiveness of the textured GZO back reflector is also demonstrated in a textured a-Si:H/μc-Si:H tandem cell with a bottom cell thickness of 2 μm, which showed higher conversion efficiency than the reference cell.