Shift Current and Ferroelectric Domain Walls in Organometal Halide Perovskites for Photovoltaic Applications

Andrew Rappe^a

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Invited Speaker, Andrew Rappe, presentation 291
Publication date: 5th February 2015

Organic-inorganic halide perovskites have attracted a great deal of attention due to their extremely rapid increase in power conversion efficiency. Tremendous efforts have been devoted to understand the reason for their high efficiency and to optimize and design more efficient materials. In particular, CH₃NH₃PbI₃ (MAPbI₃) shows the highest efficiency and also displays a large open-circuit voltage. Shift current, the main mechanism for achieving above-band-gap bulk photovoltaic effect in ferroelectric perovskites, may play an important role in providing the large open-circuit voltage in the halide perovskites. By using first-principles methods, we compute the shift current magnitude in MAPbI₃ with two different molecular orientations. We find that these materials give approximately three times larger shift current response to near-IR and visible light than the prototypical ferroelectric photovoltaic BiFeO₃. The molecular orientations of CH₃NH₃⁺ can strongly affect the corresponding PbI₃ inorganic frame and consequently alter the magnitude of the shift current response. Specifically, configurations with dipole moments aligned in parallel distort the inorganic PbI₃ frame more significantly than configurations with near-net-zero dipole, yielding a larger shift current response. Because the molecular dipole moment can give rise to macroscopic polarization in organometal halide perovskties, and particularly since switchable ferroelectric domains have been observed experimentally, we also explore the structural and electronic properties of ferroelectric domain walls in CH₃NH₃PbX₃ (X=Cl, Br, I). We find that organometal halide perovskites can form both charged and uncharged domain walls, due to the flexible orientational order of the organic molecules. It is found that the presence of charged domain walls will significantly reduce the band gap by 20%-40%, while the presence of uncharged domain walls has no substantial impact on the band gap. Furthermore, we demonstrate that charged domain walls can serve as segregated channels for the motions of charge carriers. Our findings highlight the importance of ferroelectric domain walls in hybrid perovskites for photovoltaic applications and suggest a promising approach of device optimization through domain wall engineering.

Zheng, F.; Takenaka, H.; Wang, F.; Koocher, N.Z.; and Rappe, A.M. First-principles calculations of the bulk photovoltaic effect in CH3NH3PbI3 and CH3NH3PbI3-xClx. J. Phys. Chem. Lett. 2015, 2, 31-37. Liu, S.; Zheng, F.; Koocher, N.Z.; Takenaka, H.; Wang, F.; Rappe, A.M. Ferroelectric Domain Wall Induced Band Gap Reduction and Charge 2 Separation in Organometal Halide Perovskites. J. Phys. Chem. Lett. 2015, (in press).

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