Thin film solar cells incorporating microcrystalline Si_(1-x)Ge)x as efficient infrared absorber: an application to double junction tandem solar cells

摘要

We have fabricated efficient (approx 7-8 percent) hydrogenated microcrystalline Si_(1-x)Ge_x (mu c-Si_(1-x)Ge_x:H, x approx 0.1-0.17) single junction p-i-n solar cells with markedly higher short-circuit current densities than for mu c-Si:H (x = 0) solar cells due to enhanced infrared absorption. By replacing the conventional mu c-Si:H with the mu c-Si_(1-x)Ge_x:H as infrared absorber in double junction tandem solar cells, the bottom cell thickness can be reduced by more than half while preserving the current matching with hydrogenated amorphous silicon (a-Si:H) top cell. An initial efficiency of 11.2 percent is obtained for a-Si:H/mu c-Si_(0.9)Ge_(0.1):H solar cell with bottom cell thickness less than 1 mu m.