Electron Self-Trapping in Ge 2 Se 3 and Its Role in Ag and Sn Incorporation

We present a set of density functional theory (DFT) calculations on the electronic structure of Ag and Sn in Ge 2 Se 3 in a periodic model. We show that electron self-trapping is a persistent feature in the presence of many defects. Ag and Sn autoionize upon entering Ge 2 Se 3 becoming Ag + and Sn 2+ , respectively, and the freed electrons self trap at the lowest energy site. Both Ag and Sn can substitute for Ge, and we present formation energies as a function of Fermi level that show that Sn can substantially alter the incorporation of Ag into the Ge 2 Se 3 network.