title: Local Time-Dependent Charging in a Perovskite Solar Cell.
abstract: Efficient charge extraction within solar cells explicitly depends on the optimization of the internal interfaces. Potential barriers, unbalanced charge extraction, and interfacial trap states can prevent cells from reaching high power conversion efficiencies. In the case of perovskite solar cells, slow processes happening on time scales of seconds cause hysteresis in the current-voltage characteristics. In this work, we localized and investigated these slow processes using frequency-modulation Kelvin probe force microscopy (FM-KPFM) on cross sections of planar methylammonium lead iodide (MAPI) perovskite solar cells. FM-KPFM can map the charge density distribution and its dynamics at internal interfaces. Upon illumination, space charge layers formed at the interfaces of the selective contacts with the MAPI layer within several seconds. We observed distinct differences in the charging dynamics at the interfaces of MAPI with adjacent layers. Our results indicate that more than one process is involved in hysteresis. This finding is in agreement with recent simulation studies claiming that a combination of ion migration and interfacial trap states causes the hysteresis in perovskite solar cells. Such differences in the charging rates at different interfaces cannot be separated by conventional device measurements.
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Victor W
authors.initials: VW
authors.lastname: Bergmann
authors.affiliation: Department of Chemistry, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Yunlong
authors.initials: Y
authors.lastname: Guo
authors.affiliation: Department of Chemistry, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Tanaka
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Ilka M
authors.initials: IM
authors.lastname: Hermes
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Dan
authors.initials: D
authors.lastname: Li
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Klasen
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Simon A
authors.initials: SA
authors.lastname: Bretschneider
authors.affiliation: Department of Chemistry, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Eiichi
authors.initials: E
authors.lastname: Nakamura
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Berger
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.|Institute of Physics, Johannes Gutenberg University Mainz , Duesbergweg 10-14, 55128 Mainz, Germany.
authors.forename: Stefan A L
authors.initials: SA
authors.lastname: Weber
keywords: Kelvin probe force microscopy; charge trapping; ion migration; perovskite solar cells; scanning probe microscopy; space charge layer