  The great tunability of the properties of halide perovskites presents new
opportunities for optoelectronic applications as well as significant challenges
associated with exploring combinatorial chemical spaces. In this work, we
develop a framework powered by high-throughput computations and machine
learning for the design and prediction of mixed cation halide perovskite
alloys. In a chemical space of ABX$_{3}$ perovskites with a selected set of
options for A, B, and X atoms, pseudo-cubic structures of compounds with B-site
mixing are simulated using density functional theory (DFT) and several
properties are computed, including stability, lattice constant, band gap,
vacancy formation energy, refractive index, and optical absorption spectrum,
using both semi-local and hybrid functionals. Neural networks (NN) are used to
train predictive models for every property using tabulated elemental properties
of A, B, and X site atoms as descriptors. Starting from the DFT dataset of 229
points, we use the trained NN models to predict the structural, energetic,
electronic and optical properties of a complete dataset of 17,955 compounds,
and perform high-throughput screening in terms of stability, band gap and
defect tolerance, to obtain 574 promising compounds that are ranked as
potential absorbers according to their photovoltaic figure of merit.
Compositional trends in the screened set of attractive mixed cation halide
perovskites are revealed and additional computations are performed on selected
compounds. The data-driven design framework developed here is promising for
designing novel mixed compositions and can be extended to a wider perovskite
chemical space in terms of A, B, and X atoms, different kinds of mixing at the
A, B, or X sites, non-cubic phases, and other properties of interest.
