Perylene Diimide-Based Oligomers and Polymers for Organic Optoelectronics

Abstract

ConspectusPerylene 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 clean 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 (VOC); 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 π–π 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 π–π 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.