In the field of organic optoelectronic devices polymers with donor or acceptor properties are designed by the donor-acceptor approach. Therefore, electron rich monomer units are combined with electron deficient units in order to decrease the band gap. By varying the donor as well as the acceptor strength of these monomer units the charge transport can be tuned. Our research focuses on copolymers containing thieno[3,4-c]pyrrole-4,6-dione (TPD) as electron deficient unit in combination with various comonomers based on thiophene. We chose TPD as electron deficient monomer unit mainly due to its high long-term stability, which is an important issue for the application in optoelectronic devices. Four copolymers were synthesized via Stille polycondensation in order to gain new insights into the interplay between polymer chain alignment and charge transport. The copolymerization of TPD with thiophene was conducted in two different solvents and two polymers (PTPDT) with different molecular weights were obtained. These two polymers were compared with TPD copolymers containing thieno[3,2-b]thiophene as comonomer unit (PTPDTT). All three polymers show ambipolar charge transport in OFET devices. We observed a tremendous increase in charge carrier mobilites from thiophene (from low to medium molecular weights) to thieno[3,2-b]thiophene. These results are well correlated with the polymer chain alignment studied in GIWAXS measurements. For the copolymer PTPDTT with edge-on alignment, we report the highest electron mobility of 0.17 cm2V-1s-1 in OFET for TPD containing polymers published to date. As shown in this example the polymer chain alignment plays a crucial role for high-performing materials. For OFET devices an edge-on orientation is favored, whereas face-on orientation supports charge transport in SCLC as well as OPV devices. We also show how face-on alignment can be suppressed by simply changing the processing parameters. Herein, the TPD copolymer in combination with terthiophene (PTPD3T) is studied and the results from OFET measurements can be again directly correlated with the corresponding GIWAXS measurements at different processing conditions.

Interplay between polymer chain alignment and charge transport in semiconducting polymers

254th National Meeting (2017)

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