Investigation of shunt path evolution originated from transparent conductive oxides in Si-based thin film solar cells

The evolution of the shunt path on the performance of Si-based thin film solar cells with an glass/Al-doped ZnO (AZO)/amorphous (a)-Si:H/a-SiGe:H/Al was investigated by conductive atomic force microscopy, electroluminescence measurement, and transmission electron microscopy. AZO films were highly textured for the light management before the deposition of absorption layers. The cell performance was found to be strongly dependent on the existence of nanocracks formed in a-Si:H/a-SiGe:H layers. The defects by nanocracks are expected to attribute to the leakage current in the cells. The authors introduce two types of shunt path evolution modes: pinhole defects (type A) and highly textured groove of AZO film (type B). Both crack defects by types A and B induced high leakage current, leading to a relatively reduced fill factor on the performance.