Oxide heterostructures for efficient solar cells.

We propose an unexplored class of absorbing materials for high-efficiency solar cells: heterostructures of transition-metal oxides. In particular, LaVO(3) grown on SrTiO(3) has a direct band gap ∼1.1 eV in the optimal range as well as an internal potential gradient, which can greatly help to separate the photogenerated electron-hole pairs. Furthermore, oxide heterostructures afford the flexibility to combine LaVO(3) with other materials such as LaFeO(3) in order to achieve even higher efficiencies with band-gap graded solar cells. We use density-functional theory to demonstrate these features.

Real-space mapping of electronic orbitals.

Electronic states are responsible for most material properties, including chemical bonds, electrical and thermal conductivity, as well as optical and magnetic properties. Experimentally, however, they remain mostly elusive. Here, we report the real-space mapping of selected transitions between p and d states on the Ångström scale in bulk rutile (TiO2) using electron energy-loss spectrometry (EELS), revealing information on individual bonds between atoms. On the one hand, this enables the experimental verification of theoretical predictions about electronic states. On the other hand, it paves the way for directly investigating electronic states under conditions that are at the limit of the current capabilities of numerical simulations such as, e.g., the electronic states at defects, interfaces, and quantum dots.