title: The Importance of Moisture in Hybrid Lead Halide Perovskite Thin Film Fabrication.
abstract: Moisture, in the form of ambient humidity, has a significant impact on methylammonium lead halide perovskite films. In particular, due to the hygroscopic nature of the methylammonium component, moisture plays a significant role during film formation. This issue has so far not been well understood and neither has the impact of moisture on the physical properties of resultant films. Herein, we carry out a comprehensive and well-controlled study of the effect of moisture exposure on methylammonium lead halide perovskite film formation and properties. We find that films formed in higher humidity atmospheres have a less continuous morphology but significantly improved photoluminescence, and that film formation is faster. In photovoltaic devices, we find that exposure to moisture, either in the precursor solution or in the atmosphere during formation, results in significantly improved open-circuit voltages and hence overall device performance. We then find that by post-treating dry films with moisture exposure, we can enhance photovoltaic performance and photoluminescence in a similar way. The enhanced photoluminescence and open-circuit voltage imply that the material quality is improved in films that have been exposed to moisture. We determine that this improvement stems from a reduction in trap density in the films, which we postulate to be due to the partial solvation of the methylammonium component and "self-healing" of the perovskite lattice. This work highlights the importance of controlled moisture exposure when fabricating high-performance perovskite devices and provides guidelines for the optimum environment for fabrication. Moreover, we note that often an unintentional water exposure is likely responsible for the high performance of solar cells produced in some laboratories, whereas careful synthesis and fabrication in a dry environment will lead to lower-performing devices.
authors.affiliation: Clarendon Laboratory, University of Oxford , Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: Giles E
authors.initials: GE
authors.lastname: Eperon
authors.affiliation: Clarendon Laboratory, University of Oxford , Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: Severin N
authors.initials: SN
authors.lastname: Habisreutinger
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia , via Giovanni Pascoli 70/3, 20133 Milan, Italy.
authors.forename: Tomas
authors.initials: T
authors.lastname: Leijtens
authors.affiliation: Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Bardo J
authors.initials: BJ
authors.lastname: Bruijnaers
authors.affiliation: Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands.|Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
authors.forename: Jacobus J
authors.initials: JJ
authors.lastname: van Franeker
authors.affiliation: Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States.
authors.forename: Dane W
authors.initials: DW
authors.lastname: deQuilettes
authors.affiliation: Clarendon Laboratory, University of Oxford , Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: Sandeep
authors.initials: S
authors.lastname: Pathak
authors.affiliation: Clarendon Laboratory, University of Oxford , Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Sutton
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia , via Giovanni Pascoli 70/3, 20133 Milan, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Grancini
authors.affiliation: Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States.
authors.forename: David S
authors.initials: DS
authors.lastname: Ginger
authors.affiliation: Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Rene A J
authors.initials: RA
authors.lastname: Janssen
authors.affiliation: Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia , via Giovanni Pascoli 70/3, 20133 Milan, Italy.
authors.forename: Annamaria
authors.initials: A
authors.lastname: Petrozza
authors.affiliation: Clarendon Laboratory, University of Oxford , Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Snaith
keywords: defects; fabrication; humidity; moisture; perovskite; photovoltaics; solar cell