Abstract

The formation energies, charge transition levels and quasiparticle defect states of several tin-related impurities are investigated within the DFT + GW formalism. The optical spectrum obtained from the solution of the Bethe–Salpeter equation shows that the absorption strongly increases in the sub-bandgap region after doping, suggesting a two-step photoexcitation process that facilitates transitions from photons with insufficient energy to cause direct transitions from the valence to the conduction band via an intermediate-band. We propose Sn-doped CdTe as a promising candidate for the development of high-efficiency solar cells, which could potentially overcome the Shockley–Queisser limit.