Theoretical Strategy To Design Novel n-Type Copolymers Based on Anthracene Diimide and Pyrido[2,3-g]quinoline Diimide for Organic Solar Cells.

The design and synthesis of efficient electron-transporting materials have been an active area of research in the area of organic solar cells (OSCs), organic field-effect transistors (OFETs), and organic light-emitting diodes (OLEDs). This paper is focused on designing novel n-type donor-acceptor (D-A) copolymers as electron-transporting materials for replacing the widely used fullerene acceptor materials in OSC applications. We first present a strategy which can remarkably improve the photovoltaic performances of D-A copolymer acceptors by means of adjusting the molecular planarity and intensifying the electron-withdrawing ability of electron-deficient units. Then we further analyze the role played by the D-A copolymer acceptor in the light-absorbing performance of the active layer. On the basis of two reported two D-A copolymer acceptors (PNDIT and P(NDI2OD-T2)) which are composed of an electron-deficient naphthalene diimide (NDI) unit and different electron-rich units of thiophene or bithiophene, replacement of the NDI unit with an anthracene diimide (ADI) unit and a pyrido[2,3-g]quinoline diimide (PQD) unit can produce two types of copolymer acceptors (P2, P3 and P2a, P3a). From the calculated results, the introduction of ADI and PQD units to replace the NDI unit can significantly improve the optoelectronic properties, light-absorbing efficiencies, and intermolecular electron transport abilities of the copolymers as well as exciton separation efficiencies at donor/acceptor interface. Finally, this study would give us a theoretical guidance to design efficient D-A copolymer acceptors for replacing fullerene acceptors in organic solar cells.