While high-mobility p-type conjugated polymers have been widely reported, high-mobility n-type conjugated polymers are still rare. In the present work, we designed semifluorinated alkyl side chains and introduced them into naphthalene diimide-based polymers (PNDIF-T2 and PNDIF-TVT). We found that the strong self-organization of these side chains induced a high degree of order in the attached polymer backbones by forming a superstructure composed of "backbone crystals" and "side-chain crystals". This phenomenon was shown to greatly enhance the ordering along the backbone direction, and the resulting polymers thus exhibited unipolar n-channel transport in field-effect transistors with remarkably high electron mobility values of up to 6.50 cm(2) V(-1) s(-1) and with a high on-off current ratio of 10(5).
A high-performance naphthalene diimide (NDI)-based conjugated polymer for use as the active layer of n-channel organic fi eld-effect transistors (OFETs) is reported. The solution-processable n-channel polymer is systematically designed and synthesized with an alternating structure of long alkyl substituted-NDI and thienylene-vinylene-thienylene units (PNDI-TVT). The material has a well-controlled molecular structure with an extended π -conjugated backbone, with no increase in the LUMO level, achieving a high mobility and highly ambient stable n-type OFET. The top-gate, bottomcontact device shows remarkably high electron charge-carrier mobility of up to 1.8 cm 2 V − 1 s − 1 ( I on / I off = 10 6 ) with the commonly used polymer dielectric, poly(methyl methacrylate) (PMMA). Moreover, PNDI-TVT OFETs exhibit excellent air and operation stability. Such high device performance is attributed to improved ππ intermolecular interactions owing to the extended π -conjugation, apart from the improved crystallinity and highly interdigitated lamellar structure caused by the extended ππ backbone and long alkyl groups.the morphology of the polymer fi lm, with its mixture of edge-on and face-on orientation, auto-encapsulation effect by the overlaid gate and gate dielectric layer, and low LUMO energy level of the specifi cally designed polymer.
ConclusionsWe designed and synthesized a new solution-processable n-channel polymer with an extended π -conjugated backbone, without increasing the LUMO level. The obtained polymer, PNDI-TVT, had a well-controlled alternating structure consisting of a long alkyl chain-substituted NDI as an electron acceptor unit and TVT as a donor unit. The PNDI-TVT copoly mer demonstrated a remarkably high electron-carrier mobility of up to 1.8 cm 2 V − 1 s − 1 ( I on / I off = 10 6 ) and high air and bias stress stability. To the best of our knowledge, this newly developed material showed the highest n-type mobility, in combination with excellent air and operation stabilities, among the reported n-channel conjugated polymers. The superior performance of PNDI-TVT OFET was attributed to improved ππ intermolecular interactions because of the extended π -conjugation, improved crystallinity with a highly interdigitated lamellar structure owing to the extended backbone and long alkyl groups, and mixed face-on and edge-on orientation.
A new polymeric semiconductor, PDPPDTSE, is reported which is composed of a diketopyrrolopyrrole moiety and selenophenylene vinylene selenophene, with a high field-effect mobility achieved through intermolecular donor-acceptor interactions. The field-effect mobility of OFET devices based on PDPPDTSE by spin-casting is 4.97 cm(2) V(-1) s(-1) , which is higher than predecessor polymeric semiconductors.
Interdependence of chemical structure, thin-film morphology, and transport properties is a key, yet often elusive aspect characterizing the design and development of high-mobility, solution-processed polymers for large-area and flexible electronics applications. There is a specific need to achieve >1 cm 2 V −1 s −1 field-effect mobilities (μ) at low processing temperatures in combination with environmental stability, especially in the case of electron-transporting polymers, which are still lagging behind hole transporting materials. Here, the synthesis of a naphthalene-diimide based donor-acceptor copolymer characterized by a selenophene vinylene selenophene donor moiety is reported. Optimized field-effect transistors show maximum μ of 2.4 cm 2 V −1 s −1 and promising ambient stability. A very marked film structural evolution is revealed with increasing annealing temperature, with evidence of a remarkable 3D crystallinity above 180 °C. Conversely, transport properties are found to be substantially optimized at 150 °C, with limited gain at higher temperature. This discrepancy is rationalized by the presence of a surface-segregated prevalently edge-on packed polymer phase, dominating the device accumulated channel. This study therefore serves the purpose of presenting a promising, high-electron-mobility copolymer that is processable at relatively low temperatures, and of clearly highlighting the necessity of specifically investigating channel morphology in assessing the structure-property nexus in semiconducting polymer thin films.
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