Thienoquinolinone-based acceptor-π-acceptor-type building block for polymer donors in organic solar cells

Thienoquinolinone (TQO) is a promising electron-accepting building block for donor–acceptor-type semiconducting copolymers in organic photovoltaic cells. Polymer donors comprising TQO and benzodithiophene (BDT) exhibited relatively wide bandgaps and deep frontier molecular orbital energy levels. In this study, a new TQO-based electron-accepting building block (BTQ), comprising two TQO units with a thiophene π-bridge, was designed and synthesized to induce broad absorption. Two copolymers were synthesized by Stille coupling polymerization: one comprising BDT and BTQ (PBDT-BTQ) and the other comprising fluorine-substituted BDT and BTQ (PFBDT-BTQ). These polymers showed red-shifted absorption compared to the corresponding TQO-based copolymer (PBDT-TQO) owing to extended π-conjugation. Organic photovoltaic cells based on copolymer: IT-4F were fabricated and characterized. The fabricated devices showed a maximum power conversion efficiency of 8.55