High-resolution mapping of nonuniform carrier transport at contacts to polycrystalline CdTe/CdS solar cells

Abstract

We demonstrate a spectroscopic technique based on scanning tunneling microscopy that provides high-resolution maps of local carrier transport across contacts to polycrystalline thin-film solar cells. Using this technique, preferential transport channels across a $p^{+}-\mathrm{ZnTe}\mathrm{/p-}\mathrm{CdTe}$ back contact of a $\mathrm{p-}\mathrm{CdTe}\mathrm{/n-}\mathrm{CdS}$ solar cell are imaged with 20 nm spatial resolution. Transport across this contact is highly nonuniform. Large areas of high resistance coexist with nanoscale low-resistance regions that are strongly correlated with grain boundaries in the CdTe absorber. These results suggest an important role of grain boundaries as near-contact conducting channels.