High‐Mobility Air‐Stable Naphthalene Diimide‐Based Copolymer Containing Extended π‐Conjugation for n‐Channel Organic Field Effect Transistors

Abstract

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.

Well-Balanced Carrier Mobilities in Ambipolar Transistors Based on Solution-Processable Low Band Gap Small Molecules

“…1,2 A variety of electron-rich donors, such as thiophenes 3 and selenophenes, 4−6 and electron-deficient acceptor blocks, such as isoindigos, 7−10 diketopyrrolopyrroles (DPP), 5,11−13 benzothiadiazoles, 9,14 and naphthalenedicarboximides, 15,16 have been reported. In particular, DPP acceptor blocks have received considerable attention because they form strong π−π interactions among their planar backbones and they offer high carrier mobilities exceeding 1 cm 2 V −1 s −1 .…”

Anion-induced N-doping of naphthalenediimide polymer semiconductor in organic thin-film transistors

“…Amongst the candidate conjugated n-type polymers for OTFTs, naphthalenediimide (NDI) containing copolymers have shown impressive performance to date. [30][31][32][33][34][35] For example the copolymer with bithiophene, poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-dithiophene)} (P(NDI2OD-T2)) was one of the first high performance n-type polymers. 30,36 Further improvements in performance have come from tuning the co-monomer utilised.…”

Ambipolar copolymer of dithienocoronenedi-imide and benzo(bis)thiadiazole with balanced hole and electron mobility

“…To obtain good performance of organic optoelectronic devices, balanced charge carrier transport are of great importance [2,10,[15][16][17]. To date, the majority of soluble polymers of high performance are either p-type semiconductors or n-type semiconductors [6,8,10,[18][19][20][21]. On the other hand, ambipolar polymers with balanced charge carrier transport are only a few, especially for OFET [10,15,[22][23][24].…”

“…To lower the LUMO energy levels of polymers, one strategy is to synthesize new acceptors with strong electron-drawing ability. The current polymers of appreciable electron charge carrier mobilities (>0.1 cm 2 V À1 s À1 ) span only a limited range of acceptors such as diketopyrrolo (DPP), benzo(bis)thiadiazole (BTZ), and naphthalenediimide (NDI) [4,10,18,19,21,[24][25][26]. BTZ is an acceptor with relatively low LUMO energy level.…”