Small band gap polymers based on diketopyrrolopyrrole

New small band gap polymers incorporating diketopyrrolopyrrole units have been synthesized using Suzuki and Yamamoto polymerization. By alternating the electron-deficient diketopyrrolopyrrole units with different electron-rich aromatic segments, polymers were obtained with band gaps ranging from 1.24 to 1.77 eV in thin films. In field-effect transistors these polymers exhibit ambipolar charge transport with hole and electron mobilities up to 2.1 x 10(-3) cm(2)/Vs and 1.6 x 10(-4) cm(2)/Vs, respectively. The polymers were applied as electron donor in bulk heterojunction solar cells with [60] PCBM as electron acceptor to give a maximum power conversion efficiency of 1.7% under simulated standard solar light (AM1.5G, 100 mW/cm(2)). The morphology of the bulk heterojunction blend seems to limit the photovoltaic performance.