Buffer layers for narrow bandgap a-SiGe solar cells

In high efficiency narrow bandgap (NBG) a-SiGe solar cells, thin buffer layers of unalloyed hydrogenated amorphous silicon (a-Si) are usually used at the interfaces between the a-SiGe intrinsic layer and the doped layers. We investigated the effect of inserting additional a-SiGe interface layers between these a-Si buffer layers and the a-SiGe absorber layer. We found that such additional interface layers increase solar cell V-oc and FF sizably. most likely due to the reduction or elimination of the abrupt bandgap discontinuity between the a-SiGe absorber layer and the a-Si buffer layers. With these improved narrow bandgap solar cells incorporated into the fabrication of triple-junction a-Si based solar cells, we obtained triple cells with initial efficiency of 10.6%.