|Müller, C.J.; Singh, C.R.; Fried, M.; Thelakkat, M.: High Bulk Electron Mobility Diketopyrrolopyrrole Copolymers with Perfluorothiophene, Advanced Functional Materials, 25(18), 2725–2736 (2015) -- DOI: 10.1002/adfm.201404540|
The question of designing high electron mobility polymers by increasing the planarization using diffusive nonbonding heteroatom interactions in diketopyrrolopyrrole polymers is addressed in this. For this, three different diketopyrrolo[3,4-c]pyrrole (DPP) derivatives with thienyl-, 2-pyridinyl-, and phenyl-flanked cores are copolymerized with an electron-rich thiophene unit as well as an electron-deficient 3,4-difluorothiophene unit as comonomer to obtain diverse polymeric DPPs which vary systematically in their structures. The crystallinity differs significantly with clear trends on varying both flanking unit and comonomer. The optical gap and energy levels depend more on the nature of the flanking aryl units rather than on fluorination. Additionally, the charge transport properties are compared using different methods to differentiate between interface or orientation effects and bulk charge carrier transport. In organic field effect transistor devices with very high electron as well as hole mobilities (up to 0.6 cm2 V−1 s−1) are obtained and fluorination leads to a more pronounced n-type nature in all polymers, resulting in ambipolar behavior in otherwise p-type materials. In contrast, space-charge limited current measurements show a strong influence of the flanking units only on electron mobilities. Especially, the elegant synthetic strategy of combining pyridyl flanking units with difluorothiophene as the comonomer culminates in a record bulk electron mobility of 4.3 × 10−3 cm2 V−1 s−1 in polymers.