Homogeneously Large Polarons in Aromatic Passivators Improves Charge Transport between Perovskite Grains for >24 % Efficiency in Photovoltaics

Abstract Aromatic passivators, such as porphyrin, with large π‐backbones have attracted considerable attention to boost the charge carrier in polycrystalline perovskite films, thus enabling the fabrication of efficient and stable perovskite solar cells (PSCs). However, they often self‐assemble into supramolecules that probably influence the charge‐transfer process in the perovskite grain boundary. Here, by doping a monoamine Cu porphyrin into perovskite films, two porphyrin‐based self‐assembled supramolecules were successfully prepared between perovskite grains. Crystal structures and theoretical analyses reveal the presence of a stronger interaction between the amine units and the central Cu ions of neighbouring porphyrins in one of the supramolecules. This has a modified effect on the dipole direction of the porphyrins to be quantized as homogeneously large polarons (HLPs) in a periodic lattice. The porphyrin supramolecules can stabilize perovskite grain boundaries to greatly improve the stability of PSCs, while the HLPs‐featured supramolecule facilitates hole transport across perovskite grains to remarkably increase the cell performance to as high as 24.2 %. This work proves that the modulation of the intermolecular interaction of aromatic passivators to yield HLPs is crucial for the cascaded acceleration of charge transport between perovskite grains.