Low-Cost Computing of the Thermophysical Properties of Organic–Inorganic Halide Perovskites by Density Functional Theory Combined with the Three-Dimensional Reference Interaction Site Method

Organic–inorganic
hybrid materials (OIHMs) represented by
methylammonium lead triiodide (MAPbI3) and formamidinium
lead triiodide (FAPbI3), which are the absorption layer
of perovskite solar cells, have attracted much attention. However,
it is difficult to calculate the properties of OIHMs by density functional
theory (DFT) in terms of computational cost because the organic molecules
rotate within the inorganic framework at finite temperature. Here,
using cubic MAPbI3 as an example, we demonstrate the reduction
of the computational cost for OIHMs by DFT combined with the three-dimensional
reference interaction site method (3D-RISM). The RISM was developed
to simulate the structures and reactions at the interface of solids
and liquids. By treating the MA cation as a pseudoliquid, we successfully
reproduced the distribution of the MA cation experimentally observed
at a finite temperature. When the RISM temperature was changed, the
thermal expansion coefficient and temperature dependence of the band
gap of MAPbI3 were predicted, and they were in good agreement
with experimental reports. In addition, the lattice constant, the
bandgap, and free energy of mixing of MA1–xFAxPbI3 can be evaluated
by DFT/3D-RISM without using a supercell. Therefore, this method makes
the evaluation of thermophysical properties without high-cost computing
possible.