A new easily accessible, high molecular weight, alternating dithieno-diketopyrrolopyrrolophenylene copolymer provides high electron and hole mobilities exceeding 0.02 cm(2) V-1 s(-1) in FETs and AM1.5 power conversion efficiencies of 4.6% and 5.5% in solar cells when combined with [60]PCBM and [70]PCBM. The performance of the solar cells strongly depends on the use of a processing agent.