Machine Learning Bandgaps of Inorganic Mixed Halide Perovskites

The identification of suitable lead-free perovskites is crucial for their envisioned applications in photovoltaics. Homovalent substitution of lead with Sn- and Ge-based compounds are under intense investigation as potential alternatives, but suffer from stability issues, for example, due to the susceptibility of these ions toward the 4+ oxidation state. Mixed compositions, with two or more possible ions for each lattice position, have been proposed for overcoming these issues and enhancing performance [1, 2]. However, as it is computationally and experimentally prohibitive to measure the vast configuration space available to the mixed perovskites, statistical learning techniques are needed to find a more efficient mapping of mixing parameters to the properties of interest. Efficient and accurate vetting of perovskites for a range of properties has recently been accomplished in high-throughput Density Functional Theory (DFT) studies of compounds by use of Kernel Ridge Regression (KRR) [3, 4]. Crucial to their success is the determination of adequate material fingerprints which uniquely define the materials and capture the property of interest. Here we demonstrate how one such important screening parameter, the fundamental bandgap, can be predicted for a family of inorganic mixed halide perovskites using novel globally valid material fingerprints based solely on the atomic configurations of arbitrary unit cells. The Partial Radial Distribution Function method [5] is expanded upon to include densities for a variety of elemental properties, enabling us to define a more robust material fingerprint while illuminating the underlying drivers of target properties in a chemically intuitive manner. The results are supplemented with thermodynamic and geometric data to identify the best compositions and the features responsible for them.      «

The identification of suitable lead-free perovskites is crucial for their envisioned applications in photovoltaics. Homovalent substitution of lead with Sn- and Ge-based compounds are under intense investigation as potential alternatives, but suffer from stability issues, for example, due to the susceptibility of these ions toward the 4+ oxidation state. Mixed compositions, with two or more possible ions for each lattice position, have been proposed for overcoming these issues and enhancing perf...     »