Grain boundary passivation with small polar molecules for photovoltaics

Grain boundaries (GBs) play a major role in determining the device performance of in particular polycrystalline thin film solar cells including Si, CdTe and CIGS. Hydrogen passivation has been traditionally applied to passivate the defects at GBs. However, hydrogenated films such as amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) are subject to light-induced degradation effects. In this study on multicrystalline (mc)-Si wafers, we found an excellent correlation between the grain misorientation and the corresponding electrical resistivity across grain boundaries. In particular, the charge transport across GBs was greatly enhanced after the wafers were properly treated in acetonitrile (CH3CN). The results were explained to be due to the more effective charge neutralization of polar molecules on GBs. These findings may help us achieve high-quality materials at low cost for high-efficient solar cells by improving the carrier transport and minimizing the carrier recombination. We also believe that this study will help us with a deeper understanding on GBs and their behaviors for the applications not only in photovoltaics, but also in other solid-state devices such as thin-film transistors.