Multiscale Modelling of Defects in Halide Perovskites—Implications for the Phase Stability and Degradation Reactions Induced by Thermochemical Stress

The outstanding optoelectronic properties of metal halide perovskites (MHPs) have attracted a lot of attention from the optoelectronic community recently. Despite the significant increase in efficiency, the commercialization of perovskite optoelectronic devices is hampered by long-term stability problems. This is because the common fabrication method, i.e. solution processing, is known to produce polycrystalline films with a wide variety of defects, such as point defects, surfaces and grain boundaries. Although the optoelectronic effects of these defects have been widely studied, a detailed understanding of their impact on the long-term stability, particularly an understanding of the degradation dynamics at the atomic scale, is still lacking.<br/><br/>In this presentation, I will outline our recent advances in studying the dynamical processes and their implications on the stability of halide perovskites using computational multiscale modelling. Our approach combines several levels of theory, including reactive force fields (ReaxFF) [1, 2], density functional tight-binding (DFTB) [3] and machine learned force fields (MLFF) [4]. The multiscale approach allows us to obtain important insights into the dynamical properties at the atomistic scale at various time scales, including phase transitions, phase stability, defect migration and defect-induced degradation reactions in the bulk, at surfaces and near grain boundaries for perovskites with various compositions. The atomistic insights gained in these simulations allow us to propose strategies to passivate and mitigate these defects and thereby stabilize the materials.<br/><br/>References:<br/>[1] <b>M. Pols</b>, J.M. Vicent-Luna, I. Filot, A.C.T. van Duin and S. Tao. Atomistic Insights Into the Degradation of Inorganic Halide Perovskite CsPbI₃: A Reactive Force Field Molecular Dynamics Study. J. Phys. Chem. Lett. 2021, 12, 5519-5525. DOI: https://doi.org/10.1021/acs.jpclett.1c01192.<br/>[2] <b>M. Pols</b>, T. Hilpert, I. Filot, A.C.T. van Duin, S. Calero and S. Tao. What Happens at Surfaces and Grain Boundaries of Halide Perovskites: Reactive Molecular Dynamics Simulations of CsPbI₃. Submitted. DOI: https://doi.org/10.48550/arXiv.2205.10545.<br/>[3] S. Raaijmakers, <b>M. Pols</b>, J.M. Vicent-Luna and S. Tao. Refined GFN1-xTB Parametes for Engineering Phase-Stable CsPbX₃ Perovskites. J. Phys. Chem. C 2022, 126, 22, 9587–9596 DOI: https://doi.org/10.1021/acs.jpcc.2c02412.<br/>[4] <b>M. Pols</b>, V. Brouwers and S. Tao. On-the-fly Machine Learned Force Fields for Inorganic Halide Perovskites: CsPbX₃ (X = I, Br). In preparation.