Synthesis and characterization of new selenophene-based conjugated polymers for organic photovoltaic cells

Three new polymers poly(3,4′′′-didodecyl) hexaselenophene) (P6S), poly(5,5′-bis(4,4′-didodecyl-2,2′- biselenophene-5-yl)-2,2′-biselenophene) (HHP6S), and poly(5,5′- bis(3′,4-didodecyl-2,2′-biselenophene-5-yl)-2,2′- biselenophene) (TTP6S) that have the same selenophene-based polymer backbone but different side chain patterns were designed and synthesized. The weight-averaged molecular weights (M _w) of P6S, HHP6S, and TTP6S were found to be 19,100, 24,100, and 19,700 with polydispersity indices of 2.77, 1.48, and 1.41, respectively. The UV-visible absorption maxima of P6S, HHP6S, and TTP6S are at 524, 489, and 513 nm, respectively, in solution and at 569, 517, and 606 nm, respectively, in the film state. The polymers P6S, HHP6S, and TTP6S exhibit low band gaps of 1.74, 1.95, and 1.58 eV, respectively. The field-effect mobilities of P6S, HHP6S, and TTP6S were measured to be 1.3 × 10 ^-4, 3.9 × 10 ^-6, and 3.2 × 10 ^-4 cm ² V ^-1 s ^-1, respectively. A photovoltaic device with a TTP6S/[6,6]-phenyl C ₇₁-butyric acid methyl ester (1:3, w/w) blend film active layer was found to exhibit an open circuit voltage (V _OC) of 0.71 V, a short circuit current (J _SC) of 5.72 mA cm ^-2, a fill factor of 0.41, and a power conversion efficiency (PCE) of 1.67% under AM 1.5 G (100 mW cm ^-2) illumination. TTP6S has the most planar backbone of the tested polymers, which results in strong π-π interchain interactions and strong aggregation, leading to broad absorption, high mobility, a low band gap, and the highest PCE. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 Various strategies were explored to chemically modify the selenophene backbone structure, and it was found that they lead to changes in the backbone conformation as well as in the solubility, absorption spectra, energy levels, charge transport, blend film morphology, and photovoltaic properties of the resulting polymers.