Highly crystalline polycyclic aromatic lactam-based regioregular wide-band gap polymer donors for organic solar cells

Abstract

The design of wide-band gap polymer donors with complementary absorption to non-fullerene acceptors (NFAs) is essential to increase the photovoltaic efficiency of organic solar cells (OSCs). However, some effective wide-band gap polymer donors comprising asymmetric units suffer from a lack of regioregularity, which negatively impacts the intermolecular packing among polymer backbones and decreases their degree of crystallinity and charge carrier mobility. In this study, asymmetrical electron-accepting building blocks of thienoquinolinone (TQO) or thienoisoquinolinone (TIQO) are modified to achieve dimeric structures for improving their symmetry. The different monomers are synthesized by connecting TQO and TIQO in a symmetrical dimeric structure and four kinds of wide-band gap polymer donors, namely PBDT-PQ, PBDT-TQ, PBDT-PiQ, and PBDT-TiQ, are synthesized by Stille cross-coupling polymerization with a benzodithiophene derivative. Grazing incidence wide-angle X-ray scattering (GIWAXS) results demonstrate that the synthesized polymer donors have a high degree of crystallinity. Among them, PBDT-PiQ exhibits both compact intermolecular π–π packing and a high degree of crystalline properties, which promotes effective charge transfer in the active layers. Consequently, PBDT-PiQ:Y6-based OSCs exhibit the maximum power conversion efficiency of 11.28%. The synthetic strategy proposed in this study strengthens the intermolecular interactions between polymer backbones and improves the degree of crystallinity, thereby enhancing the photovoltaic performance of OSCs.