Synthesis and electronic energy‐level regulation of imide‐fused poly(thienylene vinylene) derivatives

A series of novel poly(thienylene vinylene) derivatives (PTVs), P20-P24, with imide substituents were designed and synthesized by palladium-catalyzed Stille coupling polymerization, wherein the imide substituent density was decreased gradually, which allowed us to explicitly study the effect of electron-deficient substituent on the optical, electrochemical, and photovoltaic properties of the PTVs. All of the four polymers showed broad absorption bands with optical bandgaps between1.66 and 1.78 eV. By reducing density of electron-deficient imide group, the LUMO energy levels of the polymers could be tuned gradually from −3.75 to −3.43 eV, with HOMO levels upshifted from −5.64 to −5.16 eV. Bulk heterojunction solar cells with the polymers as donor and PC71BM as acceptor demonstrated very different excitons dissociation behavior. With decreasing the imide-fused unit density, the open-circuit voltage (VOC) values in the devices decreased from 0.78 to 0.62 V, whereas the short-circuit currents (JSC) increased from 0 to 2.26 mA cm−2 and then decreased to 1.01 mA cm−2. By adjusting the electron-withdrawing imide substituent density, power conversion efficiency of the PTVs-based solar cells can be increased to four times, reached 0.86%. To the best of our knowledge, this is the first systematic study of the relationship between molecular energy level and photovoltaic properties of PTVs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4975–4982