Non-Conjugated Flexible Linkers in Semiconducting Polymers: A Pathway to Improved Processability without Compromising Device Performance

Semiconducting polymers, in contrast to inorganic silicon, are solution processable and can potentially be printed cost efficiently on flexible large-area substrates. However to do so it is of paramount importance to formulate the polymeric semiconductors into inks with specific viscosities. Herein, the synthesis of a new highly soluble isoindigo monomer and its incorporation into low bandgap semiconducting polymers is presented. Non-conjugated flexible linkers are introduced into the conjugated backbone in order to modulate the materials processability. The viscoelastic properties of the new polymers are studied in detail by means of rheometry and dynamical mechanical analysis. The solution viscosity is directly proportional to the content of non-conjugated linkers in the polymer backbone. In organic field-effect transistors maximum hole mobilities of 1.7 cm2 V−1 s−1 are achieved with the new polymers. Due to the enhanced solubility all-polymer solar cells are fabricated by solution shearing, reaching power conversion efficiency values of 3.7%.