Modeling realistic grain boundaries in CdTe

Grain boundaries (GBs) are performance-limiting in CdTe photovoltaics. Towards understanding and improving GBs, especially in the presence of impurities or alloying elements such as Se and Cl, it is important to perform first principles density functional theory (DFT) modeling on realistic structural models. We develop and use a code FANTASTX (Fully Automated Nanoscale To Atomistic Structure from Theory and eXperiment) which aims at creating atomistic structures which are consistent with scanning transmission electron microscopy (STEM) images as well as are energetically reasonable. We will discuss the electronic structures of realistic CdTe GBs, the effects of impurities on the electronic structure, and the implications for photovoltaic performance.