π-Conjugated Main Chain Polymers Containing Bis(bithiophenyl dithienothiophene)-based Repeating Group and their Application to Polymer Solar Cells

Abstract

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 0.43–0.44 V, a short-circuit current density of 5.95–5.96 mA/cm², and a fill factor of 0.34, offering an overall power conversion efficiency (PCE) of 0.9%.

Keywords:

• Absorption
• conjugated polymers
• dithienothiophene
• mobility
• organic photovoltaics
• semiconductor

Acknowledgment

This research was supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF20100020209)