Hole-electron asymmetry in diffusion pathways induced by ferroelectric nanodomains in CH3NH3PbI3
Eduardo Menéndez-Proupin a, Ana L. Montero-Alejo a, Pablo Palacios b, Perla Wahnón b, José C. Conesa c
a Universidad de Chile, Las Palmeras 3425, Santiago, Chile
b Universidad Politécnica de Madrid, Avenidad Complutense s/n, Madrid, Spain
c Instituto de Catálisis y Petroleoquímica, CSIC, Marie Curie 2, Madrid, Spain
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics, Photonics and Optoelectronics (ABXPV18PEROPTO)
Perovskite Thin Film Photovoltaics (ABXPV18). 27-28 Feb
Rennes, France, 2018 February 27th - March 1st
Organizer: Jacky Even
Oral, Eduardo Menéndez-Proupin, presentation 032
DOI: https://doi.org/10.29363/nanoge.abxpvperopto.2018.032
Publication date: 11th December 2017

We investigate the possibility that formation of ferroelectric domains in CH3NH3PbI3 can separate the diffusion pathways of electrons and holes. This hypothesis has been proposed [1] to explain the large recombination time and the remarkable performance of the solar cells of hybrid perovskites. We find that a two-dimensional hole confinement in CH3NH3PbI3 is possible under room temperature conditions. Our models of the tetragonal phase show that the alignment of dipole layers of organic cations induces the confinement of holes but not of electrons. We find that holes can localize on PbI2 planes closest to CH3 groups. This behavior does not change even by varying the strength of the ordered dipoles. The confinement of holes is enhanced by the deformation of the inorganic PbI3 sublattice. For the conduction band electrons, the inorganic sublattice distortions counteract the effect of the oriented organic dipoles preventing the localization of the electrons. The positive charges of CH3NH3+ cations, at the locations driven by its aspherical shape, are responsible of the electron-hole asymmetry. We find that spherical cations like Cs+ cannot provide this effect. The localization/delocalization pattern in real space is reproduced in the reciprocal space. The dispersion of the top valence band is reduced in the directions perpendicular to the confinement planes, while the lowest conduction band remains isotropic.

[1] J. M Frost et al., Nano Lett. (2014), 14, 2584–2590.

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