Efficiency enhancement of a-Si:H single junction solar cells by a-Ge:H incorporation at the p+ a-SiC:H/transparent conducting oxide interface

Carbon (C) incorporation in the p+ hydrogenated amorphous silicon (a-SiC:H) is highly desirable for a-Si:H based solar cells because of the following reasons: (i) it increases the band gap of the p+ layer to ∼2 eV, which allows a majority of the sun light to pass through the thin p+ layer (∼15 nm) and get absorbed in the underlying intrinsic a-Si:H layer, and (ii) it enhances built-in potential of the a-Si:H p-i-n stack, resulting in enhanced short circuit current (JSC) and open circuit voltage (VOC). Hence, it is a desire to incorporate the highest possible C % in the p+ a-Si:H. However, C incorporation results in a Schottky barrier at the p+ a-SiC:H/transparent conducting oxide (TCO) interface, which degrades the fill factor (FF) of the solar cell. In this paper, we present a method that increases the C incorporation in p+ a-SiC:H but without adversely affecting the FF, by adding a thin layer of hydrogenated amorphous germanium (a-Ge:H) buffer at the p+ a-SiC:H/TCO interface. The presence of a-Ge:H can either minimize or eliminate the Schottky barrier. We demonstrate ∼25% enhanced efficiency of the a-Si:H solar cell by using the a-Ge:H interfacial buffer compared to that without an a-Ge:H interfacial layer.