Molecular Recognition Promotes Band Alignment in 3-D Covalent Organic Frameworks for Co-Crystalline Organic Photovoltaics

Covalent organic frameworks (COFs) have emerged as versatile, functional materials comprised of low-cost molecular building blocks. The permanent porosity, long-range order, and high surface area of 3D-COFs permit co-crystallization with other materials driven by supramolecular interactions. We designed a new subphthalocyanine-based 3-D covalent organic framework (NEUCOF1) capable of forming co-crystals with fullerene (C60) via periodic ball-and-socket binding motifs. The high co-crystalline surface area and long-range order of NEUCOF1 eliminates the typical surface area vs. structural order trade-off in organic photovoltaics (OPVs). We used plane-wave density functional theory (PBE) to minimize NEUCOF1 and NEUCOF1–C60 co-crystals and determine their electronic band structures. Molecular dynamics (MD) simulations showed that NEUCOF1–C60 is likely to be stable up to 350 K. The band structures at 0 and 350 K suggest that charge transfer to the C60 acceptors is favorable and that directional charge transport is possible for these co-crystalline OPVs.