title: Exploring the Electronic Band Structure of Organometal Halide Perovskite via Photoluminescence Anisotropy of Individual Nanocrystals.
abstract: Understanding electronic processes in organometal halide perovskites, flourishing photovoltaic, and emitting materials requires unraveling the origin of their electronic transitions. Light polarization studies can provide important information regarding transition dipole moment orientations. Investigating individual methylammonium lead triiodide perovskite nanocrystals enabled us to detect the polarization of photoluminescence intensity and photoluminescence excitation, hidden in bulk samples by ensemble averaging. Polarization properties of the crystals were correlated with their photoluminescence spectra and electron microscopy images. We propose that distortion of PbI6 octahedra leads to peculiarities of the electronic band structure close to the band-edge. Namely, the lowest band transition possesses a transition dipole moment along the apical Pb-I-Pb bond resulting in polarized photoluminescence. Excitation of photoluminescence above the bandgap is unpolarized because it involves molecular orbitals delocalized both in the apical and equatorial directions of the perovskite octahedron. Trap-assisted emission at 77 K, rather surprisingly, was polarized similar to the bandgap emission.
authors.affiliation: Chemical Physics and NanoLund, Lund University , Box 124, SE-22100, Lund, Sweden.
authors.forename: Daniela
authors.initials: D
authors.lastname: Täuber
authors.affiliation: Chemical Physics and NanoLund, Lund University , Box 124, SE-22100, Lund, Sweden.
authors.forename: Alexander
authors.initials: A
authors.lastname: Dobrovolsky
authors.affiliation: Chemical Physics and NanoLund, Lund University , Box 124, SE-22100, Lund, Sweden.
authors.forename: Rafael
authors.initials: R
authors.lastname: Camacho
authors.affiliation: Chemical Physics and NanoLund, Lund University , Box 124, SE-22100, Lund, Sweden.
authors.forename: Ivan G
authors.initials: IG
authors.lastname: Scheblykin
keywords: band structure; fluorescence microscopy; individual nanocrystal; organometal halide perovskite; photoluminescence polarization; trap-assisted emission