Synthesis of isoindigo-based oligothiophenes for molecular bulk heterojunction solar cells.

Isoindigo, as a new electron acceptor unit for organic electronic materials, was integrated into two low-energy gap oligothiophenes. Optical and electrochemical studies of the newly synthesized oligomers demonstrate broad absorption through the visible spectrum, along with appropriate energy levels, as desired for light harvesting donors for organic solar cells when blended with [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(60)BM). Molecular heterojunction solar cells were fabricated using these oligomers and exhibit a power conversion efficiency up to 1.76% with a V(oc) of 0.74 V, I(sc) of 6.3 mA/cm(2) and fill factor of 0.38.