Large-Scale Molecular Packing and Morphology-Dependent High Performance Organic Field-Effect Transistor by Symmetrical Naphthalene Diimide Appended with Methyl Cyclohexane

Abstract

The influence of structural ordering of methyl cyclohexane appended naphthalene diimide (NMeCy2) thin films and their correlation with enhanced device performances are presented here. The vacuum-deposited thin-film microstructure and morphology of NMeCy2 have been investigated using thin-film X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM) and were comparable with the bulk-phase crystalline structure and packing of NMeCy2. The organic field-effect transistor (OFET) fabricated on a glass substrate consists of a bilayer polymer dielectric poly(methyl methacrylate) (PMMA) over poly(vinyl alcohol) (PVA) and an inorganic high-k dielectric Al 2 O 3 as the third layer. NMeCy2 thermally deposited at an optimized substrate temperature (T sub ) of 60°C displayed excellent molecular packing over a large area that resulted in the improved field-effect performance with electron mobility (μ e ) value of 0.6 cm 2 V −1 s −1 and current on/off ratio (I on/off ) of 10 6 via modifications in dielectric configuration. Furthermore, the device afforded an unprecedented threshold voltage (V Th ) of 5.23 V with this material. We have been successful in developing a facile, reliable, and cheap method to tune the dielectric features which can culminate in improved field-effect transport properties. ■ INTRODUCTIONElectronic devices based on small organic molecules and polymers have received considerable attention in recent years due to their low cost and milder operating conditions. Particularly, small molecule based organic semiconductors (OSCs) are versatile, inexpensive, reliable, easily functionalized, and used as active materials in organic light-emitting devices (OLEDs), 1 organic photovoltaics (OPVs), 2 and organic fieldeffect transistors (OFETs). 3 The key problems of these molecules are the low mobility and low environmental stability. High mobility in OFETs is a prerequisite for fast response in high speed device applications. On the other hand, OFETs impose serious limitations to their practical applications due to the high operating voltage and high threshold voltage. Serious efforts have been devoted by researchers to improve these factors. This can be achieved by designing molecules with superior properties, device engineering, controlling the roughness and morphology of the dielectric, and OSC layers. The growth of OSCs and the alignment of crystalline layers on the dielectric surfaces are the key requirements for achieving high mobility. 4 Generally, the hydrophobic surface is more favorable for the growth of OSCs than hydrophilic surfaces. Highly compact well-organized molecular packing among adjacent molecules with significant π-orbital overlap and the absence of grain boundaries facilitate efficient charge transport enabling high mobility. 5 The low operating voltage is one of the main criteria for the integrated digital circuits and biosensor applications. The reduction in the threshold voltage and operating voltage can be achieved by using high-k dielectri...

Tailoring Trap Density of States through Impedance Analysis for Flexible Organic Field‐Effect Transistors

“…New organic semiconductor materials are being designed and advanced fabrication techniques are being developed for OFET. [ 7–9 ] Mobility values of OFETs are now challenging the mobility of amorphous Silicon. [ 10–13 ] For further development of a reliable OFET device, other parameters related to the dielectric layer and the dielectric/semiconductor (D/S) interface needs to be extensively studied.…”

Ultrathin Air-Stable n-Type Organic Phototransistor Array for Conformal Optoelectronics

“…prepared a near 3-μm-thick conformal 2,7-dioctyl[1]-benzothieno[3,2-b] benzothiophene (C8-BTBT)/polylactide (PLA) phototransistor that can be adhered onto a glove 4 . So far, all reports on conformable OPTs have utilized p -channel materials, mainly due to lack of n -channel organic materials with air stability and good performance 18–20 . The instability of organic radical anions in the presence of oxygen and water, or the electron traps at interfaces, is extensively believed to affect the stability of n -channel organic transistors 21,22 .…”

“…From the view of molecular design, PTCDI-C 13 H 27 is one of perylene derivatives that is favorable for the good stability in n -type organic transistors 20,26 . At the same time, PMMA is used as the dielectric of the transistor because its hydrophobic nature has been extensively shown to be favorable for good device stability 27,28 .…”

Vapor phase sensing of ammonia at the sub-ppm level using a perylene diimide thin film device

“…Frontier molecular orbital energies as estimated from cyclic voltammetry and optical absorption 0.1 M TBAPF 6 in CH 3 CN vs. Ag/AgNO 3 . b Estimated LUMO level from eqn E LUMO (eV) = À(E red onset + 4.8) = À(E pc onset À E Fc + 4.8 eV) 54. c Estimated HOMO level from eqn E HOMO = E LUMO À E optical…”