Anthradithiophene-thiophene copolymers with broad UV-vis absorption for organic solar cells and field-effect transistors

Abstract

New semiconducting copolymers, poly((TIPS-ADT)-(4,4'-didodecyl-2,2'-bithiophene)) (PTADT2) and poly((TIPS-ADT)-(2,2'-(4,4'-didodecyl-2,2'-bithiophene)dithiophene)) (PTADT4), produced by incorporating 5,11-bis(triisopropylsilylethynyl) anthra[2,3-b:7,6-b']dithiophene (TIPS-ADT) and alkyl-thiophene derivatives were synthesized via Stille coupling polymerization. The optical, electrochemical, structural, field-effect transistor, and solar cell properties of the polymers were investigated. The polymers showed good solubility at room temperature in common organic solvents due to their abundant side groups including TIPS and dodecyl side chains. Both polymers showed very broad UV absorption spectra covering the spectral range from 300 to 750 nm as a result of the combination of the different absorption ranges of the TIPS-ADT unit (short wavelength region) and thiophene derivatives (long wavelength region). The FET device fabricated using PTADT4 containing additional unsubstituted thiophene rings as a spacer between TIPS-ADT and thiophene derivatives showed a higher hole mobility (5.7 x 10-4 cm2/V s) than the PTADT2 device (2.8 x 10-5 cm2/V s), due to the improved intermolecular ordering caused by the reduced steric hindrance between bulky side chain groups. In addition, the PTADT4:(6,6)-phenyl-C70-butyric acid methyl ester (PC70BM) device showed an enhanced power conversion efficiency (PCE) of 1.30% compared with the PTADT2:PC70BM device (PCE of 0.55%) under AM 1.5G irradiation (100 mW/cm2). (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012