Molecular dynamics simulations of nucleation of hexagonal($δ$) and cubic($α$)-FAPbI$_3$ perovskites from solution

Solar to power conversion certified efficiencies of formamidinium lead iodide based single-junction perovskite solar cell is now 26%, all perovskite-perovskite tandem $\sim$28%, and the perovskite-silicon tandem solar cell is $\sim$34% going beyond gallium arsenide solar cells. Therefore, it is now one of the most promising materials for generating cheaper sunlight-based electricity. This material has two commonly known polymorphs; one is a thermodynamically stable yellow hexagonal phase. The other one is a metastable black perovskite phase: a powerful photo-active material. Thousands of experiments have been performed to produce the highly crystalline photoactive phase of formamidinium lead iodide. Despite that, PSCs often suffer from poor reproducibility and stability. One of the root cause is the lack of control over their synthesis, i.e. crystallization process, where one of the main quests is to synthesize and stabilize corner-sharing defects-free photoactive perovskite form of pure or doped black perovskite form of formamidinium lead iodide and prevent the formation of hexagonal phases. Thus, for the rapid industrialization of perovskite based solar farms to combat global rising temperatures: it is all-important to understand the polymorph selective nucleation of formamidinium lead iodide from its precursors. Towards this ultimate goal, here we perform molecular simulations of the nucleation of formamidinium lead iodide from solution. This study aims to take the primary steps for the all-atoms simulations of the polymorph selective crystallization of halide perovskites.