The effect of controllable thin film crystal growth on the aggregation of a novel high panchromaticity squaraine viable for organic solar cells

A description of the synthesis procedure is provided for a new squaraine molecule, DiPSQ(OH)2. This molecule is an interesting target molecule for organic photovoltaics (OPV) because of its unusually broad panchromaticity, suggesting a tighter molecular packing than would be expected, given its bulky alkyl side groups. UV–vis–NIR absorption data provides evidence for the presence of both H- and J-aggregates. Thin film X-ray diffraction (TFXRD) data supports the presence of one dominant crystal structure. Further interpretation of TFXRD results and complementary Atomic Force Microscopy (AFM) characterization for pure and blended samples provides a comprehensive explanation of how DiPSQ(OH)2 aggregates are affected by annealing and crystal growth. The described aggregation properties of donor–acceptor blends for solar cells are strongly dependent on annealing. Influencing phase separation, local crystallinity, and macroscopic crystallization, these physical properties are known to significantly impact charge dissociation, exciton diffusion rates, and bulk charge transport in devices. The strategy of systematically varying annealing times has resulted in improved bulk heterojunction crystallinity and regions of increased phase separation, both necessary to achieve the long term goal of morphological control for commercially viable NIR-active OPV devices.

► Synthesis for a new squaraine with tight crystal packing despite bulky side groups.
► Exciton splitting in absorbance confirms presence of J- and H-aggregates.
► Annealing increases crystallinity and J-aggregation, inferred from TFXRD, UV–vis, AFM.
► Controlling crystallinity and J-aggregation provides platform for mechanistic studies.
► J–V data are provided; the new squaraine is viable for NIR-active OPV devices.