Molecular Recognition and Band Alignment in 3D Covalent Organic Frameworks for Cocrystalline 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 3D covalent organic framework (NEU-COP1) capable of forming cocrystals with fullerene (C-60) via periodic ball-and-socket binding motifs. The high cocrystalline surface area and long-range order of NEUCOF1 eliminate the typical surface area vs long-range order trade-off in organic photovoltaics (OPVs). We used plane-wave density functional theory (PBE) to optimize NEUCOF1 and NEUCOF1-C-60 cocrystals and determine their electronic band structures. Molecular dynamics (MD) simulations showed that dispersive interactions promote co-crystallinity in NEUCOF1-C-60 and are stable up to 350 K. The band structures at 0 and 350 K suggest that there is a driving force of 0.27 eV for exciton charge transfer to the pocket-bound fullerenes. Charge separation could then occur at the COF-C60 D-A interface, followed by the transfer of the free electron to the nanowire of C-60 acceptors with a driving force of 0.20 eV.