Four small band gap semiconducting copolymers based on electron deficient diketopyrrolopyrrole alternating with electron rich trimers containing furan and benzene or thiophene have been synthesized via Suzuki polymerization. The polymers have optical band gaps between 1.4 and 1.6 eV, optimized for solar energy conversion, and exhibit ambipolar charge transport in field-effect transistors with hole and electron mobilities higher than 10-2 cm2 V-1 s-1. In solar cells the polymers are used as electron donors and provide power conversion efficiencies up to 3.7% in simulated solar light when mixed with [70]PCBM as acceptor.