title: Materials processing routes to trap-free halide perovskites.
abstract: Photovoltaic devices based on lead iodide perovskite films have seen rapid advancements, recently achieving an impressive 17.9% certified solar power conversion efficiency. Reports have consistently emphasized that the specific choice of growth conditions and chemical precursors is central to achieving superior performance from these materials; yet the roles and mechanisms underlying the selection of materials processing route is poorly understood. Here we show that films grown under iodine-rich conditions are prone to a high density of deep electronic traps (recombination centers), while the use of a chloride precursor avoids the formation of key defects (Pb atom substituted by I) responsible for short diffusion lengths and poor photovoltaic performance. Furthermore, the lowest-energy surfaces of perovskite crystals are found to be entirely trap-free, preserving both electron and hole delocalization to a remarkable degree, helping to account for explaining the success of polycrystalline perovskite films. We construct perovskite films from I-poor conditions using a lead acetate precursor, and our measurement of a long (600 ± 40 nm) diffusion length confirms this new picture of the importance of growth conditions.
authors.affiliation: Department of Electrical and Computer Engineering, The University of Toronto , Toronto, ON M5S 3G4, Canada.
authors.forename: Andrei
authors.initials: A
authors.lastname: Buin
authors.forename: Patrick
authors.initials: P
authors.lastname: Pietsch
authors.forename: Jixian
authors.initials: J
authors.lastname: Xu
authors.forename: Oleksandr
authors.initials: O
authors.lastname: Voznyy
authors.forename: Alexander H
authors.initials: AH
authors.lastname: Ip
authors.forename: Riccardo
authors.initials: R
authors.lastname: Comin
authors.forename: Edward H
authors.initials: EH
authors.lastname: Sargent
keywords: Perovskite; defect; diffusion length; electronic traps; growth; precursor