title: Substrate-controlled band positions in CH₃NH₃PbI₃ perovskite films.
abstract: Using X-ray and ultraviolet photoelectron spectroscopy, the surface band positions of solution-processed CH3NH3PbI3 perovskite thin films deposited on an insulating substrate (Al2O3), various n-type (TiO2, ZrO2, ZnO, and F:SnO2 (FTO)) substrates, and various p-type (PEDOT:PSS, NiO, and Cu2O) substrates are studied. Many-body GW calculations of the valence band density of states, with spin-orbit interactions included, show a clear correspondence with our experimental spectra and are used to confirm our assignment of the valence band maximum. These surface-sensitive photoelectron spectroscopy measurements result in shifting of the CH3NH3PbI3 valence band position relative to the Fermi energy as a function of substrate type, where the valence band to Fermi energy difference reflects the substrate type (insulating-, n-, or p-type). Specifically, the insulating- and n-type substrates increase the CH3NH3PbI3 valence band to Fermi energy difference to the extent of pinning the conduction band to the Fermi level; whereas, the p-type substrates decrease the valence band to Fermi energy difference. This observation implies that the substrate's properties enable control over the band alignment of CH3NH3PbI3 perovskite thin-film devices, potentially allowing for new device architectures as well as more efficient devices.
authors.affiliation: Chemical and Materials Sciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA. Kai.Zhu@nrel.gov Jao.vandeLagemaat@nrel.gov.
authors.forename: Elisa M
authors.initials: EM
authors.lastname: Miller
authors.forename: Yixin
authors.initials: Y
authors.lastname: Zhao
authors.forename: Candy C
authors.initials: CC
authors.lastname: Mercado
authors.forename: Sudip K
authors.initials: SK
authors.lastname: Saha
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Luther
authors.forename: Kai
authors.initials: K
authors.lastname: Zhu
authors.forename: Vladan
authors.initials: V
authors.lastname: Stevanović
authors.forename: Craig L
authors.initials: CL
authors.lastname: Perkins
authors.forename: Jao
authors.initials: J
authors.lastname: van de Lagemaat