Manipulating Methylamine Deintercalation in 2D Halide Perovskites Via Chain Length

The need for renewable power has driven the search for new spaces in which to implement photovoltaic technologies. One such space is photovoltaic windows. A potentially desirable functionality for photovoltaic windows is the ability to change transparency. To date, halide perovskites have demonstrated such a color change in addition to high photovoltaic performance. Halide perovskites, when exposed to methylamine gas, form a clear phase and return to a dark phase when the gas is driven out. This color change is the result of methylamine intercalation into the halide perovskite material, and the concomitant structural rearrangements, followed by deintercalation. Methylamine intercalation/deintercalation can result in morphological changes which would lead to photovoltaic performance loss. Thus, templating the halide perovskite structure is desirable to improve reversibility. 2D Ruddlesden-Popper phase halide perovskites with the formula A₂PbI₄ are explored and assessed for methylamine intercalation/deintercalation. Specifically, the length of the A-site organic spacer was varied to gain insight into appropriate design rules for these materials. The primary organic spacers studied are phenylalkylamines with alkyl carbon chain lengths of 0, 2, and 4 between the phenyl ring and ammonium head group. With varying chain lengths, there are differing intermolecular interactions between the carbon chains in the dielectric layer of the 2D halide perovskite and thus differing molecular forces. It is found that 2D perovskites with weak intermolecular interactions in this organic dielectric layer retain significant amounts of methylamine and show greater, irreversible, structural changes upon methylamine intercalation/deintercalation. Ultimately a better understanding is gained of how differing A-site organic spaces can template the 2D halide perovskite structure and lead to more reproducible intercalation and deintercalation of MA gas. This provides improved understanding of the complex interactions in 2D halide perovskites and provides a step toward improved color switchable perovskite solar cells.