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DNA based chemical sensor for the detection of nitrogen dioxide (NO 2 ) enabled by organic field-effect transistor (OFET) was fabricated. In this OFET-based chemical sensor, DNA was introduced between the gate dielectric and the organic semiconducting layer via spray-coating to function as the detecting layer for NO 2 analyte. Comparing with the OFET without the DNA interlayer, an enhanced sensing performance of OFET with the DNA interlayer was observed when exposed to various concentrations of NO 2 analyte. The sensitivity of the OFET-based sensor with DNA interlayer was nearly one order of magnitude higher than that of the controlled device. The results showed that there were the remarkable shifts of saturation current and charge carrier mobility after exposed to NO 2 analyte. By analyzing the electrical characteristics, and the morphologies of the dielectrics and pentacene films of the OFET-based sensors, the performance enhancement was ascribed to the negatively charged phosphate groups in DNA molecules, which could interact with NO 2 analytes and lead to a superior sensing performance of OFET incorporating with DNA. [ABSTRACT FROM AUTHOR]

Poly(3-hexylthiophene) (P3HT):polystyrene (PS) blends prepared from different solvents were used as the semiconducting layers in organic field-effect transistors (OFETs). The relationship between the molecular arrangement, aggregation and charge transport in P3HT:PS blends with the boil-points and solubility of different solvents were systematically analyzed. Topographic investigation by atomic force microscopy carried out on blends with various solvents revealed a lateral phase separation of the two components, which was strongly influenced by the choice of solvent. Although the blend film was highly disordered, the OFETs performed as well as that with the pristine P3HT films. Moreover, 1,2-dichlorobenzene with the high boiling temperature was found to be more desirable for achieving distinct lateral aggregation of P3HT in the blend film, which led to the superior performance of the OFET. X-ray diffraction analyses and optical absorption measurements revealed that PS matrix made the arrangement of P3HT molecules more disordered, but introduced a more efficient intermolecular coupling of P3HT molecules. This could be ascribed to that, the PS matrix made the aggregating rates of the P3HT molecules slower, inducing a uniform distribution of P3HT molecules in the blend film. This was beneficial for the efficient charge transport in the blend film, which provided a pathway between the aggregations and acted as a tie-molecule in the blend film. Consequently, the field-effect mobility of the optimized OFET (1.6 wt% P3HT) increased three times and the current on/off ratio increased two times compared to that of the pure P3HT (8 wt%). This work will fill the gap of current research about semiconductor/insulator blend transistor. [ABSTRACT FROM AUTHOR]

Abstract: Ammonia (NH3) sensors based on bottom contact organic field-effect transistors (OFETs) were created using pentacene as an active layer and polymerthylmethacrylate (PMMA) as an insulator. The OFET sensors exhibited a change in the electric characteristic such as the threshold voltage, the saturation current, and the field-effect charge carrier mobility when the sensors were exposed to different NH3 concentrations. Meanwhile, the favorable and rapid NH3 response characteristics of the OFET sensors were observed from the change in the drain-source current as a function of time, when the sensors were exposed to various cycles of exposure/evacuation of different NH3 concentrations ranging from 10 to 100ppm. Moreover, the environmental stability of the OFET sensors to constantly detect the NH3 gas in air was studied by storing the sensors in air for 30days. [Copyright &y& Elsevier]

Abstract: Top contact pentacene field-effect transistors (OFETs) with or without MoO3 source/drain (S/D) electrodes buffer layers were fabricated by utilizing different deposition rates of Au S/D electrodes. The results showed that the characteristics of these OFETs have a strong dependence on the deposition rate of Au S/D electrodes. More importantly, single pentacene layer OFETs with optimized Au deposition process exhibits significantly improved performance, which is almost equal to the OFETs with MoO3 buffer layers. The high performance of OFETs with optimized Au deposition process was attributed to an improved contact of Au and pentacene caused by ordered dipole arrangement at the interface, leading to a nearly non-injection barrier of charge carriers from Au electrodes to pentacene. [Copyright &y& Elsevier]

Organic field-effect transistors (OFETs) with a heterojunction structure, consisting of the p-type and n-type organic semiconducting materials of copper phthalocyanine (CuPc) and the dioctyl perylene tetracarboxylic diimide (PTCDI-C8), respectively, were fabricated. The heterojunction OFETs were used as the nitrogen dioxide (NO 2 ) gas sensors, and the sensing properties were characterized with the variation of PTCDI-C8 layer thicknesses. The results showed that the OFET sensors with the optimized film thickness of 0.5 nm PTCDI-C8 and 7 nm CuPc, had one order of magnitude enhancement of sensitivity, compared to the device with single CuPc active layer. The sensitivity improvement was attributed to the intensification of the charge transfer in the heterojunction structure while introducing the oxidizing gas of NO 2 . [ABSTRACT FROM AUTHOR]

High performance low-voltage pentacene-based organic field-effect transistors (OFETs) are fabricated utilizing solution-processed alumina (Al 2 O 3 ) as high-k gate dielectric, and the effects of gate dielectric capacitance on the device performance were investigated. The results show that Al 2 O 3 gate dielectric with optimized thickness can afford OFETs performance with field-effect mobility of 0.65 cm 2 /Vs, threshold voltage of −0.6 V, I on / I off ratio of 4 × 10 3 and sub-threshold swing of 0.45 V/dec, at operating voltage as low as −4 V. After employing a very thin PMMA film onto Al 2 O 3 , the mobility of these OFETs with bilayer dielectric can be further boost up to 0.84 cm 2 /Vs. According to electrical and microscope characterizations, the performance improvement of OFETs can be contributed to low surface trap density and high capacitance density of Al 2 O 3 /PMMA bilayer dielectrics. [ABSTRACT FROM AUTHOR]

Highlights: [•] OFET based ammonia gas sensors with various polymer dielectrics are fabricated. [•] PS based OFET exhibits reliable recovery property and detect limitation of 1ppm. [•] Preferable surface property of PS is responsible for the high-performance. [Copyright &y& Elsevier]

Despite their favorable electronicand structural properties, thesynthetic development and incorporation of thiazole-based buildingblocks into n-type semiconductors has lagged behindthat of other π-deficient building blocks. Since thiazole insertioninto π-conjugated systems is synthetically more demanding, continuousresearch efforts are essential to underscore their properties in electron-transportingdevices. Here, we report the design, synthesis, and characterizationof a new series of thiazole–thiophene tetra- (1and 2) and hexa-heteroaryl (3and 4) co-oligomers, varied by core extension and regiochemistry,which are end-functionalized with electron-withdrawing perfluorohexylsubstituents. These new semiconductors are found to exhibit excellent n-channel OFET transport with electron mobilities (μe) as high as 1.30 cm2/(V·s)(Ion/Ioff>106) for films of 2deposited at room temperature.In contrary to previous studies, we show here that 2,2′-bithiazolecan be a very practical building block for high-performance n-channel semiconductors. Additionally, upon 2,2′-and 5,5′-bithiazole insertion into a sexithiophene backboneof well-known DFH-6T, significant charge transport improvements(from 0.001–0.021 cm2/(V·s) to 0.20–0.70cm2/(V·s)) were observed for 3and 4. Analysis of the thin-film morphological and microstructuralcharacteristics, in combination with the physicochemical properties,explains the observed high mobilities for the present semiconductors.Finally, we demonstrate for the first time implementation of a thiazolesemiconductor (2) into a trilayer light-emitting transistor(OLET) enabling green light emission. Our results show that thiazoleis a promising building block for efficient electron transport inπ-conjugated semiconductor thin-films, and it should be studiedmore in future optoelectronic applications. [ABSTRACT FROM AUTHOR]