Ultrafast optical snapshots of hybrid perovskites reveal the origin of multiband electronic transitions

Hybrid organic-inorganic perovskites are a promising class of materials for low-temperature solution-processed thin-film optoelectronic technologies. Here, the authors assign the visible and near-infrared optical transitions in large-grain thin films, using variable temperature transient absorption measurements that provide a sensitive probe of the electronic energy levels. These studies address an ongoing controversy concerning the nature of higher-order subband transitions. The strong visible absorption band is assigned to nearly degenerate transitions originating from different momentum states within the multivalley electronic band structure using symmetry analysis and the response of the optical resonances during the low-temperature structural phase transition.