Engineering Flat and Dispersive Bands in 2D Layered COFs via Interlayer Stacking and Donor–Acceptor Strategy

Covalent organic frameworks (COFs) are an emergent class of two-dimensional (2D) crystalline organic materials that exhibit unique electronic, optical, and transport properties. In this study, we employ density functional theory (DFT) and the Multiparticle Holstein Formalism (MHF) to investigate the electronic structure and the two-dimensional coherence of polarons in donor–acceptor COFs as a function of the interlayer stacking arrangement. We show that simple modifications in the interlayer stacking arrangement have a profound impact on the transport properties, which can range from metallic behavior with a vanishing band gap to highly localized states having flat bands. The extent of charge delocalization is found to be sensitive to the type of stacking arrangement and to the precise arrangement of the donor and acceptor fragments within the COF structure. The results from the DFT calculations are consistent with MHF-based simulations, demonstrating that stacking-induced interlayer interactions may facilitate better intraframework charge delocalization. As a consequence, we find that interlayer interactions can help circumvent defect-induced trap states to enhance the overall charge delocalization. Based on these analyses, we conclude that interlayer stacking can be exploited to guide the design of new 2D layered COF structures, with potential applications in organic electronics.