Hybrid organic-inorganic perovskites have attracted the attention of the photovoltaic research community during the past five years due to their promising performance as light harvesting material. In particular, CH3NH3PbI3 (MAPI) is the prototypical example on which most of the experimental work has been done and the system that we have selected to perform this computational study consisting of molecular dynamics simulations based on forces calculated from density functional theory. The complexity of the system represents a serious challenge for the first principles MD simulation technique, as it involves a relatively large number of atoms and long timescales. The dynamical behavior of the MA molecules in the cubic phase shows an interesting behavior as revealed by first principles molecular dynamics simulations. There is a strong finite size effect: 2x2x2 and 4x4x4 simulation boxes display a slower MA rotational relaxation dynamics than 3x3x3 and 5x5x5 boxes. Moreover, there is no attenuation of this effect between the smallest and largest boxes. The odd-even effect can in principle be attributed to a frustrating coupling of the image boxes imposed by the periodic boundary conditions. Nevertheless, other possibilities involving a wrong energy scale of the underlying DFT model will be discussed.
Marcelo A. Carignano
Qatar Environment and Energy Research Institute (QEERI)
Hamad Bin Khalifa University
P.O. Box 5825, Doha, Qatar
http://www.qeeri.org.qa/