High-Throughput Methods for Lead-Free Halide Double Perovskites: Computation and Experiment

Lead-free halide double perovskites (LFHDP) have been an emerging material class for various applications in the field of optoelectronics over the last couple of years. In contrast to their lead-based counterparts they possess not only tunable optoelectronic properties but environmental friendliness and exceptional stability.^[1-2] Nevertheless only a small number of those perovskites have been evaluated up until today. The material class can be enlarged even further by substituting the Pb²⁺ ion not only with one M¹⁺ and one M³⁺ ion but with two of each resulting in a total number of six ions in the material.^[3-5] This adaption increases the number of possible materials immensely and gives rise to the demand for a different approach in material investigation: high-throughput (HTP) screening.<br/>HTP screening aims to analyze a vast material range in a reasonable time by applying automation techniques and the restriction to swift measurement methods. Overcoming this issue can be done by applying not only HTP experimental methods but also HTP computational methods. Density functional theory (DFT) is able to examine a perfectly controlled range of material compositions for complementary features.<br/>The combination of these strategies is a promising approach towards a HTP screening in novel materials discovery and is shown to be applicable on the example of Cs₂Ag_xNa_(1-x)Bi_yIn_(1-y)Cl₆. DFT has access to features like e. g. the lattice parameter, elastic properties and electronic properties whereas experimental methods investigate e. g. optical and vibrational material properties. By combining these two screening approaches a wider picture of the full material properties can be achieved.<br/>Additionally DFT is not restricted by synthesis conditions and can therefor give an indication of what to expect of materials on the composition map which are not easily synthesizable or just reducing the time consumption of a certain measurement if only a random sample of the material range is measured and those measurements are then used as a calibration for the density functional data received for the whole composition map.<br/>Using the variety of ion combinations in this LFHDP structure with interchangeable ion ratios opens up a whole new field of materials which can be evaluated by the methods developed on the example of Cs₂Ag_xNa_(1-x)Bi_yIn_(1-y)Cl₆and therefor to build up a database. Using machine learning algorithms on this database can lead to a deeper understanding of the coupling between the ion exchange and macroscopic material properties.<br/>Sources:<br/>[1] E. Meyer, D. Mutukwa, N. Zingwe, and R. Taziwa, “Lead-Free Halide Double Perovskites: A Review of the Structural, Optical, and Stability Properties as Well as Their Viability to Replace Lead Halide Perovskites,” Metals, vol. 8, no. 9. MDPI AG, p. 667, Aug. 27, 2018. doi: 10.3390/met8090667.<br/>[2] L. Chu et al., “Lead-Free Halide Double Perovskite Materials: A New Superstar Toward Green and Stable Optoelectronic Applications,” Nano-Micro Letters, vol. 11, no. 1. Springer Science and Business Media LLC, Feb. 27, 2019. doi: 10.1007/s40820-019-0244-6.<br/>[3] H. Tang et al., “Lead-Free Halide Double Perovskite Nanocrystals for Light-Emitting Applications: Strategies for Boosting Efficiency and Stability,” Advanced Science, vol. 8, no. 7. Wiley, Mar. 03, 2021. doi: 10.1002/advs.202004118.<br/>[4] S. Li, J. Luo, J. Liu, and J. Tang, “Self-Trapped Excitons in All-Inorganic Halide Perovskites: Fundamentals, Status, and Potential Applications,” The Journal of Physical Chemistry Letters, vol. 10, no. 8. American Chemical Society (ACS), pp. 1999–2007, Apr. 04, 2019. doi: 10.1021/acs.jpclett.8b03604.<br/>[5] O. Stroyuk et al., “‘Green’ synthesis of highly luminescent lead-free Cs2AgxNa1−xBiyIn1−yCl6 perovskites,” Journal of Materials Chemistry C, vol. 10, no. 27. Royal Society of Chemistry (RSC), pp. 9938–9944, 2022. doi: 10.1039/d2tc02055f.