We report on organic n-channel field-effect transistors and circuits based on C 60 films grown by hot wall epitaxy. Electron mobility is found to be dependent strongly on the substrate temperature during film growth and on the type of the gate dielectric employed. Top-contact transistors employing LiF / Al electrodes and a polymer dielectric exhibit maximum electron mobility of 6 cm 2 / V s. When the same films are employed in bottom-contact transistors, using SiO 2 as gate dielectric, mobility is reduced to 0.2 cm 2 / V s. By integrating several transistors we are able to fabricate high performance unipolar ͑n-channel͒ ring oscillators with stage delay of 2.3 s. To date hole transporting ͑p-type͒ organic small molecules and polymers are by far the most widely used materials for the fabrication of functional organic circuits based on unipolar logic architectures [1][2][3][4][5][6][7][8][9] . Electron transporting ͑n-type͒ organic semiconductors on the other hand have received considerably less attention 2,10 with very few circuit demonstrations.11 This is mainly due to the poor operating stability of the vast majority of electron transporting organic field-effect transistors ͑OFETs͒ under ambient conditions with only few exemptions. [12][13][14][15][16] Among the relatively few known electron transporting molecules is the C 60 fullerene with electron mobility, measured in oxygen and water free environment, on the order of 1 cm 2 /V s. [17][18][19] Despite the high performance, however, C 60 based transistors degrade rapidly upon exposure to ambient air. 11,18 In an effort to overcome this problem Horiuchi et al. 20 have reported on an efficient oxygen passivation method using a top coating of alumina layer sputtered under Ar atmosphere. As a result the stability of C 60 transistors was considerably improved and showed no degradation upon exposure to air for a period of one month. This finding has renewed interest on fullerenes and use of C 60 can now be envisioned not only in organic unipolar circuits but also in the much needed complementary architectures. 15,21,22 To this end a primary challenge is the further improvement of the operating characteristics of C 60 OFETs and the demonstration of functional integrated circuits.Here we report on high mobility electron transporting ͑n-channel͒ organic transistors and circuits based on C 60 films grown by hot wall epitaxy ͑HWE͒. 17,23,24 Making use of this technique and in combination with suitable gate dielectrics, we are able to fabricate discrete electron transporting transistors and integrated ring oscillators with excellent performing characteristics.Discrete top-contact transistors were fabricated on quartz glass substrates incorporating a predefined indium tin oxide ͑ITO͒ electrode acting as the gate terminal. Divinyltetramethyldisiloxane-bis͑benzocyclobutene͒ ͑BCB͒, purchased from Dow Chemicals, was spin coated on the top of the quartz/ITO substrate as the gate dielectric. Following, a 300 nm thick film of C 60 was grown by hot wall epitaxy 17 with the substr...
Ambipolar organic semiconductors enable complementary-like circuits in organic electronics. Here we show promising electron and hole transport properties in the natural pigment Tyrian Purple (6,6’-dibromoindigo). X-ray diffraction of Tyrian Purple films reveals a highly-ordered structure with a single preferential orientation, attributed to intermolecular hydrogen bonding. This material, with a band gap of ∼1.8 eV, demonstrates high hole and electron mobilities of 0.22 cm2/V·s and 0.03 cm2/V·s in transistors, respectively; and air-stable operation. Inverters with gains of 250 in the first and third quadrant show the large potential of Tyrian Purple for the development of integrated organic electronic circuits
Novel hole‐transporting dendrimeric molecules containing dioctylfluorene, spirobi(fluorene) and spiro(cylododecane‐fluorene) as the core unit and different numbers of carbazole and thiophene moieties as the peripheral groups are synthesized. All the dendrimers are characterized by 1H NMR, 13C NMR, FTIR, UV–vis, PL spectroscopy, and MALDI‐TOF. They are thermally stable with high glass transition and decomposition temperatures and exhibit chemically reversible redox processes. They are used as the hole‐transporting layer (HTL) material for multilayer organic light emitting diodes (OLEDs) with a low turn‐on voltage of around 2.5 V and a bright green emission with a maximum luminance of around 25400 cd m−2.
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