Silaindacenodithiophene Semiconducting Polymers for Efficient Solar Cells and High-Mobility Ambipolar Transistors

New silaindacenodithiophene (SiIDT) semiconducting polymers were reported. Two repeat units were selected for copolymerization. Polymers P-1 and P-2 were both synthesized by Stille cross coupling, using microwave heating conditions. Polymerizations proceeded in good yield when the stannyl groups were located on the electron rich SiIDT, with sufficiently high molecular weights obtained. Both polymers show evidence of crystallinity when evaluated by differential scanning calorimetry (DSC). By replacing the BT unit (P-1) with DPP (P-2), a redshifted absorption spectrum with more defined vibronic structure is obtained. The deep HOMO level ensures that the P-1 is stable against electrochemical oxidization, and thus good device life times can be expected. Both as-spun and annealed P-2 FET devices show clear ambipolar characteristics. These polymers can exhibit either high solar cell efficiencies of greater than 4% PCE, or high ambipolar charge transport, with holes and electrons exhibiting mobilities of greater than 0.1 cm2/(V s).