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Liquid crystalline phthalocyanines, metalized and metal-free, were investigated in order to evaluate their applicability as semiconducting active layer in optoelectronic devices. They present a stable rectangular columnar plastic mesophase at room temperature after cooling down from the isotropic liquid. Previous studies demonstrated high rectification with moderate charge carrier mobility in a diode structure under unfavorable edge-on alignment, as a result of the strong π-π interactions exhibited by close molecular packing of the mesophase. The spontaneous dominant alignment of the columns parallel to the substrate is desired for application in field effect transistors. The optical, structural and morphological properties of the compounds in spin-coated films demonstrated potential for good charge transport in-plane direction. The output characteristics of a field effect transistor with the copper phthalocyanine are consistent with the literature, and could be improved by thermal treatment. [ABSTRACT FROM PUBLISHER]

To enhance the field-effect mobility, we tried to control the interchain distance (or packing density of polymer chains) in polydiacetylene thin films by changing the side chain length of diacetylene monomers. We selected five different alkyl chain lengths of diacetylene monocarboxylic acid. An OFET device was prepared by a vacuum deposition of diacetylene monomer, followed by a photopolymerization under Xe-lamp excitation (bottom-contact type device). In this series of samples, we obtained a maximum field-effect mobility of 4.4 × 10-2 cm2/Vs in the OFET using 10, 12-heptacosadiynoic acid (HDA). Controlling the substrate temperature from 28 to 70°C, we found the optimum substrate temperature of 40°C for HDA monomer deposition, and obtained a high field-effect hole mobility of 0.1 cm2/Vs in the bottom source-drain electrode configuration. [ABSTRACT FROM AUTHOR]

A comparative study of hole-mobility in N,N'-diphenyl-N,N'-di(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) using three independent measurement techniques is presented. Time-of-flight (TOF), steady-state space charge-limited current (SCLC) experiments are carried-out in neat films of TPD, sandwiched between electrodes with different work functions. Organic field-effect transistors (OFET) are fabricated from TPD thin films and their electrical properties characterized. The comparative results show that all-electrical measurements that involve carrier injection from a metal electrode into the organic film yield effective mobility values that are one order of magnitude lower than those obtained from time-of-flight experiments in which carriers are created in the film optically. Similarly, SCLC and TOF experiments were used to measure electron-mobility in a discoid organic compound 2,3,8,9,14,15-hexakis-dodecylsulfanyl-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA-(SC12H25)6). [ABSTRACT FROM AUTHOR]

We fabricated a photo field effect transistor (photo FET) having a poly (N-vinyl carbazole) (PVK) insulator layer. PVK was employed as a photosensitive insulator material for the Photo FET. In this photo FET, illumination of a blue light to the PVK insulator drastically improved the field effect mobility and the gate-switching ratio. This result would be due to that the photo-generated carriers in the PVK layer were effectively accumulated in the gate capacitor of the photo FET. [ABSTRACT FROM AUTHOR]