Poly([2,6'-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]{3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7-Th) is a semiconducting polymer with a narrow band gap of 1.59 eV and an absorption peak at 780 nm. The devices fabricated from PTB7-Th have been shown to have…