We report here the synthesis and characterization of a new series of semiconducting polymers based on dithieno[3,2-b:2,3'-d]sioloe (SiDT) copolymerized with cyanated oligothiophenes (-2T- or -4T-) units. The effect of the fine structural tuning of the thiophene-based spacer on optical, electronic, morphological, and photophysical properties of the resulting polymers is investigated and correlated with the organic photovoltaic (OPV) performance. Bulk heterojunction (BHJ) solar cells, using this class of copolymers as electron donor material, are fabricated, optimized, and fully characterized. As a result of rational structural modifications, PCEs of similar to 5% and open circuit voltages (V-OC) greater than 0.8 V are achieved without the need of additional thermal annealing.