Theoretical Design of Perylene Diimide Dimers with Different Linkers and Bridged Positions as Promising Non-Fullerene Acceptors for Organic Photovoltaic Cells

Abstract

The intermolecular stacking and crystallization of perylene diimides (<b>PDIs</b>) has become research obstacles for small molecule acceptors (SMAs). For breaking molecular rigidity and planarity, it is an executable way to increase the distortion between two <b>PDI</b> units. A class of <b>PDI</b> dimers were designed via bridging different linkers in bay positions (1–1′ bridge) and headland positions (1–2′ bridge) to screen suitable acceptor materials for organic photovoltaic cells (OPVs). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to investigate their electronic structures, open circuit voltage (<i>V</i>_OC), driving forces (Δ<i>E</i>_L‑L), and some major parameters related to the short-circuit current density (<i>J</i>_SC) such as absorption spectrum and carrier transport ability. Meanwhile, the intermolecular charge transfer (inter-CT) and charge recombination (inter-CR) rates were calculated for a further analysis on charge transfer properties at donor/acceptor (D/A) interface by employing the Marcus semiclassical model. The results manifest that the investigated 1–2′ bridged molecules possess low-lying LUMO energy levels, relatively bigger Δ<i>E</i>_L‑L, bathochromic-shifted absorption, as well as the strongest maximum absorption and more effective charge transport than 1–1′ bridged molecules. Surprisingly, compared with <b>P3HT</b>/(1–1′ bridged <b>PDI</b> dimers) interface, almost constant reorganization energy (λ), higher Gibbs free energy change of exciton dissociation (Δ<i>G</i>_CT), and considerable inter-CT/inter-CR rates ratios (<i>k</i>_inter‑CT<i>/k</i>_inter‑CR) of P3HT/(1–2′ bridged <b>PDI</b> dimers) provides further evidence for that 1–2′ bridged <b>PDI</b> dimers as acceptors might perform higher efficiency in OPV device. Moreover, constructing <b>NDT</b> and <b>DPPT</b> as bridged linkers in <b>PDI</b> dimers as “push–pull” structures may rationally expect more favorable properties as acceptors in OPVs, which might provide theoretical guideline for the design and synthesis of new organic SMAs