Vibronic Structure in Room Temperature Photoluminescence of the Halide Perovskite Cs3Bi2Br9

We report a study on the optical properties of the layered polymorph of vacancy-ordered triple perovskite Cs3Bi2Br9. The electronic structure, determined from density functional theory calculations, shows the top of the valence band and bottom of the conduction band minima are, unusually, dominated by Bi s and p states, respectively. This produces a sharp exciton peak in the absorption spectra with a binding energy that was approximated to be 940 meV, which is substantially stronger than values found in other halide perovskites and, instead, more closely reflects values seen in alkali halide crystals. This large binding energy is indicative of a strongly localized character and results in a highly structured emission at room temperature as the exciton couples to vibrations in the lattice

Anionic order and band gap engineering in vacancy ordered triple perovskites

We demonstrate that the optical absorption of the vacancy-ordered triple perovskite, Cs3Bi2Br9, can be significantly red-shifted by substituting Br with I while maintaining the layered structural topology. We also present evidence that Br ions prefer to occupy the bridging halide position within the layers in order to minimize strain within the lattice that results from the incorporation of the significantly larger iodide anions into the lattice. These results not only quantify the upper limit for I content in the layered polymorph, but also establish the minimum band gap obtainable from these Bi-based phases

Charge separation at nanostructured molecular donor–acceptor interfaces

Planar and bulk heterojunctions of organic donor and acceptor molecules are used to understand elementary processes in photovoltaic cells. The electronic structure, interface and film morphology, excitonic behavior, device characteristics, and correlations between these properties are reviewed here using a wide range of material combination