Molecular interaction modulating Ruddlesden-Popper tin-based perovskite crystallization

Ruddlesden-Popper (RP) tin-based halide perovskites have attracted intensive attention because of unique properties such as low-toxicity and low-cost processability. However, the uncontrollable crystallization of RP tin-based perovskites from solvents leads to less perfect crystal orientation and thus poor absorber layers with pinholes. Here, we propose an effective method to slow down crystallization kinetics via regulating the competition between intra- and intermolecular interactions in RP tin-based perovskites. Introducing an electron-rich heterocyclic thiophene rather than the traditional benzene ring into bulky spacers (i.e., 2-thiophenemethylammonium cation, abbreviated as TH+) can decrease the intermolecular interaction between iodostannic sheets and spacer cations but increase intramolecular interactions in spacer cations. A weak intermolecular interaction increases the strength of electrostatic repulsion between charged colloids, and thus stabilizes colloids. Such stable colloids could retard sol-gel transition before crystal formation, offering a wider processing window for orderly crystal growth of RP tin-based perovskites. The interlayer heterocyclic spacer interaction induces a subsequently ordered self-assembly of gels to reduce morphological defects. The TH(2)FA(3)Sn(4)I(13) perovskite solar cell exhibits a two-fold improvement in power conversion efficiency compared to the control sample.