Alternating polymers based on alkoxy-phenyl substituted indacenodithiophene and fluorinated quinoxaline derivatives for photovoltaic cells

To effectively modulate the molecular energy levels of indacenodithiophene (IDT)-based donor-acceptor (D-A) polymers, 4-hexyloxy-phenyl and 3-fluorine-4-hexyloxy-phenyl substituted IDT derivatives were designed and copolymerized with fluorinated quinoxaline derivatives (0F, 1F and 2F) to construct a series of novel alternating polymers. The effects of the side-chain modification in IDT units and the inclusion of fluorine atoms on quinoxaline units on the absorption performances, energy levels, hole transporting properties and photovoltaic performances of the resulting polymers were systemically studied. All polymers show high molecular weight, good solubility in common solvents, excellent thermal stabilities, finely tunable bandgaps and gradient adjusted energy levels. Above 5 % power conversion efficiencies (PCEs) were achieved for all six polymers in conventional structural solar cells blending with [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM), in which the 3-fluorine-4-hexyloxy-phenyl substituted IDT and quinoxaline based polymer (FO-TQ) showed a high PCE of 5.97 % due to its high hole mobility and suitable energy level.