π-Conjugated main chain polymers containing bis(bithiophenyl dithienothiophene)-based repeating group and their application to polymer solar cells

New dithienothiophene (DTT)-containing conjugated polymers, such as poly(2,6-bis(2-thiophenyl-3-dodecylthiophene-2-yl)dithieno[3,2-b;2',3'-d] thiophene, 1 and poly(2,6-bis(2-thiophenyl-4-dodecylthiophene-2-yl)dithieno[3,2- b;2',3'-d]thiophene, 2 have been successfully synthesized via Stille coupling reactions using dodecyl-substituted thiophene-based monomer, bistributyltin dithienothiophene, and bistributyltin bithiophene. The main difference between two polymers is the substitution position of dodecyl side chains in a repeating group. The semiconducting properties of the two polymers have been evaluated in organic photovoltaics (OPVs). Two conjugated polymers are also well mixed with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) for fabricating bulk heterojunction PV devices. As a result, the polymer solar cell devices made of polymers 1 and 2 had the best preliminary results with an open-circuit voltage of 0.43-0.44V, a short-circuit current density of 5.95-5.96mA/cm², and a fill factor of 0.34, offering an overall power conversion efficiency (PCE) of 0.9%.