Methoxy-substituted thiophene units were incorporated into a diketopyrrolopyrrole and quaterthiophene based copolymer to produce random copolymers. Inclusion of the methoxy group narrowed the optical energy gap of the resulting copolymers owing to the enhanced planar backbone that results in more effective conjugation. At a low loading ratio of 25mol% random copolymer exhibited a hole mobility of ~0.3 cm2 V−1 s−1 comparable to that of the diketopyrrolopyrrole and quaterthiophene based original polymer. Although increasing the methoxy-substituted thiophene ratio in the polymers resulted in decreased molecular weights, it was concluded that incorporation of the methoxy-substituted thiophenes enhanced the hole mobility from 0.02 cm2 V−1 s−1 for 50mol% loading to 0.07 cm2 V−1 s−1 for 100mol% loading. The enhancement was attributed to the formation of pre-aggregates with stronger interchain interactions with increasing backbone coplanarity, resulting in edge-on dominant and bimodal edge-on/face-on molecular packing orientations. The addition of tetramethylammonium iodide as an ionic additive proved not to be an effective method for improving the performance of polymers containing the methoxy-substituted thiophenes, whereas the original polymer displayed a noticeable improvement of the charge transport properties.
- Organic field effect transistor
- Random conjugated polymer
- Structure-property relationship