Fluorinated thienyl-quinoxaline-based D–π–A-type copolymer toward efficient polymer solar cells: synthesis, characterization, and photovoltaic properties

Abstract

A tailor-made donor–π–acceptor copolymer comprising of a medium electron-donating alkylthienyl-benzodithiophene (BDTT) moiety and a strong electron-accepting fluorinated thienyl-quinoxaline (TTFQ) segment with thiophene π-bridge units has been synthesized by Stille coupling polymerization and thoroughly characterized for use as a p-type semiconducting polymer. The semicrystalline copolymer PBDTT-TTFQ shows a broad visible-near-infrared absorption band with an optical bandgap of 1.67 eV and possesses a relatively low-lying HOMO level at −5.34 eV. In addition, the PBDTT-TTFQ neat film reveals a highly dense fibrillar nanostructure with a certain degree of long-range order, suggesting the nanoscale self-assembly of PBDTT and TTFQ segments. A bulk-heterojunction polymer solar cell based on the blend of 1 : 1 PBDTT-TTFQ:PC₇₁BM shows an open circuit voltage of 0.75 V, a short circuit current density of 14.6 mA cm⁻², and a fill factor of 56.1%, achieving a power conversion efficiency of 6.1% under the illumination of AM 1.5G, 100 mW cm⁻². The results unambiguously indicate that the PBDTT-TTFQ is an auspicious candidate for next-generation solar cell materials.