Introducing an isolated intermediate band (IB) into a wide band gap semiconductor can potentially improve the optical absorption of the material beyond the Shockley-Queisser limitation for solar cells. Here, we present a systematic study of the thermodynamic stability, electronic structures, and optical properties of transition metals (M = Ti, V, and Fe) doped CuAlSe 2 for potential IB thin film solar cells, by adopting the first-principles calculation based on the hybrid functional method. We found from chemical potential analysis that for all dopants considered, the stable doped phase only exits when the Al atom is substituted. More importantly, with this substitution, the IB feature is determined by 3d electronic nature of M 3+ ion, and the electronic configuration of 3d 1 can drive a optimum IB that possesses half-filled character and suitable subbandgap from valence band or conduction band. We further show that Ti-doped CuAlSe 2 is the more promising candidate for IB materials since the resulted IB in it is half filled and extra absorption peaks occurs in the optical spectrum accompanied with a largely enhanced light absorption intensity. The result offers a understanding for IB induced by transition metals into CuAlSe 2 and is significant to fabricate the related IB materials.
The electronic structure of stoichiometric tin dioxide (SnO 2 ) is studied by probing its unoccupied states using the fine structure in the electron energy-loss spectra (EELS) at the oxygen K-edge. The spectral measurements were made both at room-and high temperature (773 K), and compared to ab initio calculations carried out using real-space multiple scattering and linearized augmented-plane wave methods. Important many-body effects are included via quasiparticle corrections calculated within the many-pole GW self-energy approximation. An additional energy dependent damping is calculated to account for vibrational effects. Results from this study demonstrated that quantitative agreement between theoretical and experimental spectra can be obtained when non-spherical potentials and quasiparticle self-energy effects are considered, and vibrational broadening is included. Modifications of the electronic structure by single oxygen vacancies, both in the bulk and at the (110) surface, are also predicted. Our predictions support the use of O-K EELS as a probe of defect structure in SnO 2 surfaces and nanoparticles.
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