Solution-Processable Organic Photovoltaic Cell Based on the Oligothiophene with Solubilizing β-alkyl Groups

We synthesized a linear pi-conjugated small molecule (beta-DH5T) based on thiophene, using the palladium-catalyzed Suzuki coupling. The oligothiophene was designed to contain beta-substituted solubilizing alkyl groups to facilitate solution processing. The organic photovoltaic cell based on beta-DH5T:PC71BM gave a power conversion efficiency of 0.46% with a short-circuit current of 4.69mA/cm(2), an open-circuit voltage of 0.60V, and a fill factor of 0.35, giving under AM 1.5G illumination (100mW/cm(2)). The optical and electrochemical properties and molecular alignment of oligothiophene were investigated using UV-visible absorption spectroscopy, cyclic voltammetry, and thin-film X-ray diffraction studies.