Alternative Thieno[3,2-b][1]benzothiophene Isoindigo Polymers for Solar Cell Applications.

This work reports the synthesis, characterization, photophysical, and photovoltaic properties of five new thieno[3,2-b][1]benzothiophene isoindigo (TBTI)-containing low bandgap donor-acceptor conjugated polymers with a series of comonomers and different side chains. When TBTI is combined with different electron-rich moieties, even small structural variations can have significant impact on thin film morphology of the polymer:phenyl C70 butyric acid methyl ester (PCBM) blends. More importantly, high-resolution electron energy loss spectroscopy is used to investigate the phase-separated bulk heterojunction domains, which can be accurately and precisely resolved, enabling an enhanced correlation between polymer chemical structure, photovoltaic device performance, and morphology.