Transferable Classical Force Field for Pure and Mixed Metal Halide Perovskites Parameterized from First-Principles

Area of Science:

• Materials Science
• Computational Chemistry
• Solid-State Physics

Background:

• Photovoltaic perovskites exhibit complex behaviors over long timescales and with mixed compositions, necessitating accurate yet computationally efficient models.
• Existing models often lack the simplicity or transferability required for diverse perovskite systems.

Purpose of the Study:

• To develop a transferable classical force field for mixed hybrid perovskites (MAFA_1-Pb(BrI_1-)₃) applicable to variable compositions.
• To enable realistic and numerically simple simulations of ion migration dynamics in these materials.

Main Methods:

• Utilized Lennard-Jones, Buckingham, and AMBER potentials for inter- and intramolecular interactions.
• Employed a genetic algorithm, previously developed for CsPb(BrI_1-)₃, to parameterize the force field against DFT energies.
• Performed classical molecular dynamics simulations with up to 8600 atoms and 40 ns duration.

Main Results:

• The force field accurately reproduces X-ray diffraction (XRD) patterns and lattice expansion upon I/Br substitution.
• Calculated ion diffusion coefficients for pure and mixed perovskites using a fully dynamical method.
• Obtained theoretical upper limits for ion migration dynamics, excluding defects like grain boundaries.

Conclusions:

• The developed transferable force field is a significant advancement for simulating mixed perovskite systems.
• This model provides crucial insights into ion migration mechanisms, essential for optimizing photovoltaic device performance.
• The reported ion diffusion coefficients offer a benchmark for understanding operational dynamics in perovskite solar cells.