Novel Solution Process for High-Mobility C$_{60}$ Fullerene Field-Effect Transistors

Abstract

Solution-processed C 60 fullerene field-effect transistors with high electron mobility were demonstrated by using a novel drying process. Highly uniform and flat C 60 layers were prepared from a C 60 solution when the solution was rapidly dried in a vacuum chamber. Field-effect transistors with solution-deposited C 60 active layers showed electron mobility of up to 0.86 cm 2 V À1 s À1 , threshold voltage of 3 V, subthreshold slope of 0.67 V/decade, and a current on/off ratio of 4 Â 10 6 . The mobilities of solution-deposited C 60 transistors were comparable to those of vacuumdeposited C 60 transistors. # 2011 The Japan Society of Applied Physics O rganic field-effect transistors (OFETs) have attracted much interest due to their high field-effect mobilities comparable to those of amorphous silicon transistors, and for their applications in large-area sensor arrays, radio-frequency identification tags, and backplanes for flexible displays. 1-3) In addition, an advantage of OFETs is that the channel material can be deposited by a solution process.Carbon 60, C 60 , is a very promising material that provides high electron mobilities of up to 6 cm 2 V À1 s À1 . 4) Many research groups have demonstrated C 60 FETs with high mobilities of more than 1 cm 2 V À1 s À1 , which were realized using top-and bottom-contact configuration. 5,6) However, it is difficult to obtain uniform C 60 thin-film layers prepared by a solution process. The difficulty of using a solution process to produce C 60 thin films is attributed to the low solubility of C 60 in organic solvents and their high crystallinity. Some groups have used functionalized C 60 derivatives to enhance solubility. 7-11) However, the performance of FETs with C 60 derivatives was quite poor compared with that of FETs with vacuum-deposited layers of unsubstituted C 60 . Although C 60 is soluble in benzene derivatives such as toluene, mxylene, 1,2,4-trichlorobenzene, and 1,2,3,4-tetrahydronaphthalene, 12-16) the high crystallinity of C 60 17,18) remains a problem for the solution process. Thus, there have been only a few reports of C 60 FETs fabricated by solution processes. C 60 spin-coated on polymer gate insulators 19) and polymer/ C 60 blends 20) were used as channel materials for the C 60 FETs. The mobilities were 0.21 cm 2 V À1 s À1 for the spincoated C 60 and 0.01 cm 2 V À1 s À1 for the polymer/C 60 blends. Although these approaches provide thin-film layers from solution, the mobilities are lower than those of C 60 FETs obtained by vacuum evaporation.In this paper, we report a novel solution process for C 60 layers to fabricate FETs. We obtained highly uniform and flat C 60 thin-film layers when drying a C 60 solution on a substrate in a vacuum chamber at room temperature. The drying process was applied to fabricate C 60 FETs. In addition, the C 60 layer was patterned by forming solutionwettable and unwettable self-assembled monolayers (SAMs). 21) The measured field-effect mobilities in the saturation regime ranged from 0.58 to 0.86 cm 2 V À1 s À1 , slightly dependan...

Solution-processed n-type fullerene field-effect transistors prepared using CVD-grown graphene electrodes: improving performance with thermal annealing

“…Previous studies revealed that the C 60 crystals formed a face-centered cubic ( fcc) phase structure. 15,17,39 The relationship between the crystallinity and T A was further explored and an in-depth analysis of the crystalline structure of the C 60 thin films prepared on graphene was conducted by collecting 2D-GIXD measurements. Fig.…”

“…13,14 However, the studies on the solution-processable C 60 -based FETs reported to date have focused only on the effects of surface modifications on the insulating layer and solvent dependence of the formation of a stable C 60 thin film, and the electron transfer properties. [15][16][17] As the field progresses, understanding the characteristics of electrode/semiconductor interfaces has become important because the crystallinity of the semiconductor deposited on electrodes may depend on the surface properties of the electrodes in a bottomcontact configuration. Source/drain (S/D) electrodes are typically patterned prior to the deposition of an organic semiconductor layer.…”

Design molecular rectifier and photodetector with all-boron fullerene

“…Fullerene molecules such as C 60 and C 70 have been the subject of intensive research during the past decades due to their intriguing structural, electronic and optical properties [1][2][3][4][5][6][7][8][9][10]. The search for possible fullerene-like molecules has attracted more and more attention.…”

Polaron Structure and Transport in Fullerene Materials: Insights from First-Principles Calculations

“…Of the various materials that have been explored as possible electron acceptors in FETs, C 60 fullerenes ,,− and C 70 fullerenes and their derivatives have been used in a large number of studies and have shown some of the more promising electron mobilities . C 70 has also been studied extensively as an electron-acceptor in OPVs, − with C 70 -based acceptors offering increased photoabsorption over a large energy range relative to the traditional C 60 -based acceptors .…”