Molecular Recognition and Band Alignment in 3D Covalent Organic Frameworks for Cocrystalline Organic Photovoltaics
Jordan M. Cox, Bradley Mileson, Ananthan Sadagopan, Steven A. Lopez
Abstract
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 (NEUCOF1) capable of forming cocrystals with fullerene (C60) 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–C60 co-crystals and determine their electronic band structures. Molecular dynamics (MD) simulations showed that dispersive interactions promote co-crystallinity in NEUCOF1–C60 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 C60 acceptors with a driving force of 0.20 eV.