Electronic structure of formamidinium ions in lead triiodide perovskites

Perovskite formamidinium lead triiodide (FAPbI(3)) is a very promising photovoltaic material. Unfortunately, perovskite FAPbI(3) converts to a hexagonal phase at ambient conditions. Herein we study the electronic structure of both perovskite and hexagonal FAPbI(3) films using soft X-ray absorption near edge structure (XANES) and density functional theory. We find that the C and N 2p states of FA hybridize with the Pb, I states at the conduction band minimum in hexagonal, but not perovskite, FAPbI(3). We also demonstrate that C K-edge XANES can be used to investigate shifts in the valence band in other organic-inorganic hybrid perovskites. [GRAPHICS] Graphical summary of the electronic structure and C K-edge XANES in both perovskite and hexagonal FAPbI(3) highlighting our findings. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim