Effect of Pendant Functionality in Thieno[3,4‑b]thiophene-alt-benzodithiophene Polymers for OPVs

The performance of organic photovoltaics (OPVs) is heavily dependent on the structure and functionalization of the conjugated polymer used in the active absorbing layer. Using a set of materials based on poly­(thieno­[3,4-b]­thiophene-alt-benzodithiophene) with different alkyl, aryl, perfluoroalkyl, and perfluoroaryl pendant functionalities, we have studied the correlation between absorbance, morphology, crystallinity, charge mobility, and the OPV performance in an effort to identify structure-performance relationships. The perfluorinated pendants on PTF8B and PTFPB were shown to significantly enhance the V_oc in the OPV devices (by ∼0.2 V), but also induced the formation of larger phase separated PCBM-rich domains. PT8B and PTFPB devices reached average efficiencies of ∼3.2%.