Diketopyrrolopyrrole-Based Conjugated Oligomers And Their Organic Thin-Film Transistors

Conjugated oligomers are characterized by well-defined structures,absence of batch-batch variations and ease of purification.The introduction of donor-acceptor?D-A?character can also endow the oilgomers other advantages,such as easy modulation of energy levels and strong intermolecular interactions.However,there is only a few conjugated oligomers with mobility over 1 cm²V^-1s^-1 reported to date.The relatively low mobility of conjugated oligomers may be attributed to the presence of large amount of grain boudaries in their films,which can noticeably limit the transport of charge carriers.Considering this problem,the current thesis proposed to improve the film quality and thereby enhance the performance of organic thin-film transistors?OTFTs?by blending a small amount of polymers.Three D-A conjugated oligomers based on diketopyrrolopyrrole?DPP?and three polymers,i.e.,conjugated oligomer based rod-coil polymer P1,poly?methyl methacrylate??PMMA?and DPP-based conjugated polymer PDPPBT,were selected.The relationship between film morphology of blend films and OTFT performance with molecular structures and blend ratios was studied.The main results are as follows:?1?Three rod-coil polymers with DPP-based D-A conjugated oligomers as rod?P1,P2 and P3?were synthesized.Their film morphology,film microstructures and OTFT performance were studied.The polymer P1 delivered the best device performance with hole mobility up to 2.4x10-3 cm²V^-1s^-1 after annealing at 200 oC for 15 minutes.?2?OTFT performance of three D-A conjugated oligomers?O1,O2 and O3?with DPP and thienoacenes as A and D units,respectively,were studied.They all are p-type semiconductors and their OTFT mobility is enhanced with the increase of the size of thienoacenes.O3 exhibited the highest mobility(0.20 cm²V^-1s^-1).Film morphology studies indicate that low film continuity and obvious grain boudaries are main factors limiting the efficient charge carriers transport.?3?The relationship between film morphology and OTFT perfromance of O1,O2 and O3 after the addition of P1?PMMA and PDPPBT were studied.No OTFT mobility enhancement was observed when P1 was used.In contrast,the device performance was noticeably improved when the oligomers were blended with PMMA and PDPPBT.The mobility of O3 was enhanced to 0.30 cm²V^-1s^-1 when 1 wt% PMMA was added,and those of O2 and O3 were raised to 0.44 and 0.34 cm²V^-1s^-1,respectively,when 5 wt% PDPPBT was added.This mobility elevation is ascribed to the improvement of film quality such as enhanced film continuity and decreased grain boudaries.Packing structures of the oligomers in film state was almost not influenced by adding the polymers.