Impact of dipole orientation on the band gap of Perovskites: A density functional study
Ferdinand Grozema a, Tom Savenije  a, Nicolas Renaud a, Sudeep Maheshwari a
a Delft University of Technology, Julianalaan 136, Delft, 2628, Netherlands
nanoGe Perovskite Conferences
Proceedings of Perovskite Thin Film Photovoltaics (ABXPV)
Barcelona, Spain, 2016 March 3rd - 4th
Organizers: Emilio Palomares and Nam-Gyu Park
Poster, Sudeep Maheshwari, 075
Publication date: 14th December 2015
In this study we have examined the impact of dipole orientation on the electronic structure of lead-iodide perovskites containing different organic cations: methylammonium, formamidinium, guanidinium, hydrazinium and hydroxylammonium. These cations have different dipole moments and thus provide an interesting platform to asses the importance of dipole-dipole and charge-dipole interactions in perovskites.
We have performed geometry optimizations of the different perovskite systems at the DFT level of theory using van der Waals-corrected exchange-correlation functionals (GGA-D3). A cubic lattice with uniform dipole orientations was assumed to perform the geometry optimization conserving the shape of the lattice. We have subsequently calculated the electronic structure of different super-cells containing 2-4 unit cells. Our study shows that the total energy as well as the value of the band gaps varies significantly with the precise orientation of the dipoles within the super cell. As a consequence calculations relying on uniform orientation of dipoles may incorrectly estimate the value of the band gaps of these promising materials.The orientation of the dipoles also has an effect on the charge density of valence and conduction bands.

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