Colloidal chemistry of MAPbI₃ perovskite ink using 2-methoxyethanol as the solvent

Solvent is vital in determining the colloidal chemistry of perovskite ink. A depth understanding on the colloidal chemistry is essential to fine-regulate the crystallization of perovskite film. A low-polar solvent, 2-methoxyethanol (2-Me), shows growing potential than the traditional high-polar solvents in scaling-up perovskite solar cells, owing to the fast evaporation rate and the ability to form perovskite films without anti-solvent. However, as a relatively new solvent, the colloidal chemistry has not been fully understood. Here, the colloidal chemistry of fresh and aged perovskite ink using 2-Me as the solvent is investigated. The as-composed perovskite ink is characteristic of weakly bonded I^- ions and the existence of cluster complexes. In the fresh perovskite ink, the weakly bonded I^- ions enhance the dissolution of methylammonium (MA⁺), and also induce the formation of I₃^- ions in the diluted or aged solution. Both iodoplumbate species and cluster complexes are dispersed by MA⁺ ions in the solution, however, the former transforms to clusters after aging. These changes results in increased crystal size and non-uniform coverage in the perovskite film. These findings provide valuable insights into the optimization of perovskite ink using 2-Me as the solvent.