Molecular Doping of a High Mobility Diketopyrrolopyrrole- Dithienylthieno[3,2-b]thiophene Donor-Acceptor Copolymer with F6TCNNQ

Herein we present a molecular doping of a high mobility diketopyrrolopyrrole dithienylthieno[3,2-b]thiophene donor-acceptor copolymer poly[3,6-(dithiophene-2-yl)-2,5-di(6-dodecyloctadecyl)-pyrrolo [3,4-c]pyrrole-1,4-dione-alt-thien o [3,2-b)] thioph en e], PDPP (6-DO)(2)TT, with the electron-deficient compound hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ). Despite a slightly negative HOMOdonor-LUMOacceptor offset of -0.12 eV which may suggest a reduced driving force for the charge transfer (CT), a partial charge CT was experimentally observed in PDPP(6-DO)(2)TT:F6TCNNQ by absorption, vibrational, and electron paramagnetic resonance spectroscopies and predicted by density functional theory calculations. Despite the modest CT, PDPP(6-DO)(2)TT:F6TCNNQ films possess unexpectedly high conductivities up to 2 S/cm (comparable with the conductivities of the benchmark doped polymer system P3HT:F4TCNQhaving a large positive offset). The observation of the high conductivity in doped PDPP(6-DO)(2)TT films can be explained by a high hole mobility in PDPP(6-DO)(2)TT blends which compensates a lowered (relatively to P3HT:F4TCNQ) concentration of free charge carriers. We also show that F6TCNNQ-doped P3HT, the system which has not been reported so far to the best of our knowledge, exhibits a conductivity up to 7 S/cm, which exceeds the conductivity of the benchmark P3HT:F4TCNQ system.