Adv. Mater. http://doi.org/f2c6ch (2013)

The morphological organization and crystallinity of conjugated polymers can be engineered to modify their electronic properties: this has been widely applied in organic electronics, with the aim of improving the charge-transport performance of transistors and, more recently, the power-conversion efficiency of organic solar cells. Yue Wu and colleagues now apply molecular design to improve the structural regularity of a highly efficient organic semiconductor polymer known as PBDTTT, which usually adopts an amorphous configuration. The authors modify the molecular structure of the monomers composing this organic material, and achieve new polymer chains with a linear backbone conformation. Absorption spectra and X-ray diffraction patterns collected from deposited thin films made of this reshaped conjugated polymer show enhanced interchain packing and π–π stacking, which lead to a more crystalline morphology. Such improved regularity is reflected in the performance of bulk heterojunction solar cells: the authors obtain devices with a 30% increased efficiency when they replace PBDTTT with the linear polymer as the electron-donor material in polymer–fullerene blends.