title: Impedance Spectroscopic Indication for Solid State Electrochemical Reaction in (CH3NH3)PbI3 Films.
abstract: Halide perovskite-based solar cells still have limited reproducibility, stability, and incomplete understanding of how they work. We track electronic processes in [CH3NH3]PbI3(Cl) ("perovskite") films in vacuo, and in N2, air, and O2, using impedance spectroscopy (IS), contact potential difference, and surface photovoltage measurements, providing direct evidence for perovskite sensitivity to the ambient environment. Two major characteristics of the perovskite IS response change with ambient environment, viz. -1- appearance of negative capacitance in vacuo or post-vacuo N2 exposure, indicating for the first time an electrochemical process in the perovskite, and -2- orders of magnitude decrease in the film resistance upon transferring the film from O2-rich ambient atmosphere to vacuum. The same change in ambient conditions also results in a 0.5 V decrease in the material work function. We suggest that facile adsorption of oxygen onto the film dedopes it from n-type toward intrinsic. These effects influence any material characterization, i.e., results may be ambient-dependent due to changes in the material's electrical properties and electrochemical reactivity, which can also affect material stability.
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Arava
authors.initials: A
authors.lastname: Zohar
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Nir
authors.initials: N
authors.lastname: Kedem
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Igal
authors.initials: I
authors.lastname: Levine
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Dorin
authors.initials: D
authors.lastname: Zohar
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Ayelet
authors.initials: A
authors.lastname: Vilan
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Ehre
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Gary
authors.initials: G
authors.lastname: Hodes
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Cahen
keywords: contact potential difference; halide perovskite solar cells; impedance spectroscopy; surface photovoltage