Tailored Supramolecular Additives to Control the Crystallization Process and Morphology of MAPbI₃

Perovskite films feature unique optoelectronic properties, rendering them promising for electronic devices. The properties depend on the morphology on a broad range of length scales from nanometers to millimeters, influenced by a variety of factors. However, controlling the morphology is challenging. A tailored supramolecular additive, N, N'-bis(2-aminoethyl) terephthalamide is developed to control the intermediate and perovskite crystallization of methyl ammonium lead iodide (MAPbI₃) and enhance the thermal and moisture stability in the final film. Reversible coordinative interactions of the carbonyl groups with Pb²⁺ ions via Lewis acid-base adduct and subsequent ion-ion interactions of the peripheral ammonium groups with the perovskite grain boundaries are combined which is stabilized by a strong hydrogen bonding pattern formed between the amide moieties of the additive molecules. Adding low amounts of this additive to the precursor solution significantly decelerates the structure formation and systematically reduces the crystallite size. Slower growth of the intermediate phases and the incorporation of the additive to the grain boundary is observed with multiple time-resolved techniques. Evidence for the formation of single-molecule interlayers between the MAPbI₃ crystals and the presence of directed supramolecular interaction between additive molecules is shown. Transferability of this approach to other perovskites is anticipated, paving the way to improved processing control and stability.