Impact of Film Stoichiometry on the Ionization Energy and Electronic Structure of CH sub(3)NH sub(3)PbI sub(3 ) Perovskites

The electronic structure of a large sample set of CH sub(3)NH sub(3)PbI sub(3 )-based perovskites is studied. Combined investigations by UV/X-ray photoelectron spectroscopy and X-ray diffraction reveal that interstitials present in the film lead to changes in the occupied density of states close to the valence band, which in turn influences the performance of solar cells. Changes in elemental composition tune the ionization energy of the perovskite film by almost 1 eV without introducing significant amounts of gap states.