Why Do Eight Units of Methylammonium Enclose PbI6 Octahedron in Large-Scale Crystals of Methylammonium Lead Iodide Perovskite Solar Cell? An Answer from First-Principles Study

Methylammonium lead triiodide (CH3NH3PbI3) perovskite solar cell is a gem in the list of photovoltaic semiconductors. Although there are numerous fundamental and technological questions yet to be addressed covering various aspects of this system for its commercialization, this study has employed first-principles DFT to model the [PbI6(CH3NH3)n]m zero-dimensional nanoclusters. Using the calculated binding energy landscapes, it has answered the question: why the corner-sharing PbI6 octahedron is surrounded by eight units of the organic cation in the large-scale supramolecular structures of the CH3NH3PbI3 system in 3D? The synergistic effect of the methylammonium, as well as the consequence of positive and negative cooperative effects associated with intermolecular hydrogen bonding on the supramolecular evolution of the CH3NH3PbI3 crystals is briefly outlined.