Ferroelectric domains in methylammonium lead iodide perovskite solar cells

Holger Röhm^a, Tobias Leonhard^a^,^b, Michael J. Hoffmann^b^,^c, Alexander Colsmann^a^,^b

^aLight Technology Institute, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany

^bMaterial Research Center for Energy Systems, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany

^cInstitute for Applied Materials – Ceramic Materials and Technologies, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting 2018 (NFM18)

S7 Fundamental Aspects of Perovskite Solar Cells and Optoelectronics

Torremolinos, Spain, 2018 October 22nd - 26th

Organizers: Laura Herz and Tze-Chien Sum

Oral, Holger Röhm, presentation 167
DOI: https://doi.org/10.29363/nanoge.nfm.2018.167
Publication date: 6th July 2018

Within five years, methylammonium lead iodide (MAPbI3) solar cells have quickly reached remarkable power conversion efficiencies rivaling those of established technologies. However, arguably, the toxic and water-soluble lead compound may be an obstacle on their way to market. The quest for alternative, non-toxic photo harvesters is partly hampered by a lack of fundamental understanding of the crystal grain’s characteristics and energy conversion mechanisms. As part of this process, the scientific community controversially discusses the importance of ferroic properties for the exceptional performance of MAPbI3 light-harvesting layers, including claims of non-ferroelectricity, anti-ferroelectricity, ferroelectricity and ferroelasticity. Simulations have predicted ferroelectricity in MAPbI3 with alternating polarized domains ruling the charge carrier transport [1]. Understanding the crystallographic cause and the effects of the crystal’s ferroelectricity would therefore provide helpful guidance for the quest to find non-toxic MAPbI3 replacements.

We explore the ferroic properties of methylammonium lead iodide perovskite solar cells by piezoresponse force microscopy (PFM) [2][3]. In vertical and horizontal PFM imaging, we find 90 nm wide ferroelectric domains of alternating polarization. High-resolution photo-conductive atomic force micrographs under illumination also show alternating charge carrier extraction patterns which we attribute to the local vertical polarization components within the ferroelectric domains.

We apply these techniques to investigate formation of polarized domains during thermal treatment and study their influence on the performance of perovskite solar cells. Annealing steps, commonly only viewed as a means of crystal growth and precursor conversion, prove to directly influence the formation, shape and polarization direction of ferroelectric domains in perovskite thin films.

References:

[1] D. Rossi, A. Pecchia, M. Auf der Maur, T. Leonhard, H. Röhm, M. J. Hoffmann, A. Colsmann, A. D. Carlo, Nano En. (2018).

[2] H. Röhm, T. Leonhard, M.J. Hoffmann, A. Colsmann, Energy Environ. Sci. (2017).

[3] T. Leonhard, A. Schulz, H. Röhm, S. Wagner, F. Altermann, W. Rheinheimer, M.J. Hoffmann, A. Colsmann, submitted.

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