Perylene Diimide-Based Oligomers and Polymers for Organic Optoelectronics

Perylene diimide (PDI) as a classical dye has some advantages, such as structural diversity, tunable optical and electronic properties, strong light absorption, high electron affinity, and good electron-transporting properties and stability. The PDI-based oligomers and polymers are good candidates for n-type semiconductors in organic electronics and photonic devices. A polymer solar cell (PSC) that converts sunlight into electricity is a promising renewable and dean energy technology and has some superiorities, such as simple preparation and being lightweight, low cost, semitransparent, and flexible. For a long time, fullerene derivatives (e.g., PCBM) have been the most important electron acceptors used in the active layer of PSCs. However, PCBM suffers from some disadvantages, for example, weak absorption, a large amount of energy loss, and unstable morphology. Compared to PCBM, PDI-based materials present some advantages: intense visible-light absorption; lowest unoccupied molecular orbital (LUMO) energy levels can be modulated to achieve a suitable charge separation driving force and high open-circuit voltage (V-OC); and the molecular configuration can be adjusted to achieve morphology stability. Thus, PDI-based oligomers and polymers are widely used as electron acceptors in the active layer of PSCs. In addition, PDI-based oligomers and polymers are widely used as n-type semiconductors in other electronic and photonic devices, such as organic field-effect transistors (OFETs), light-emitting diodes, lasers, optical switches, and photodetectors. In this Account, we present a brief survey of the developments in PDI-based oligomers and polymers and their applications in organic electronic and photonic devices, especially in solar cells and field-effect transistors. Although parent PDI dyes exhibit strong absorption, large electron affinity, and high electron mobility, the initial bulk-heterojunction PSCs based on PDI acceptors yielded a very low power conversion efficiency (ca. 0.1%). The highly planar configuration of parent PDI causes strong intermolecular pi-pi stacking, large crystalline domains, and severe donor/acceptor (D/A) phase separation, leading to a low exciton dissociation efficiency and poor device performance. Starting in 2007, our group designed linear-shaped PDI dimers with different bridges, star-shaped PDI trimers, and PDI polymers to overcome excess crystallization and PDI aggregation and to achieve appropriate D/A miscibility and phase separation. Molecular design strategies were developed to promote the planarity of the backbone and down- shifted LUMO level of PDI polymers, which is beneficial for strong intermolecular pi-pi stacking, high mobility, and good air stability of OFETs. Beyond PSC and OFET applications, PDI polymers can also be used in perovskite solar cells and two-photon absorption. Future research directions toward the performance optimization of PDI oligomers and polymers are also proposed.