P-channel Semiconductor Research Articles

Utilization of simply alkylated diketopyrrolopyrrole derivative as a p-channel semiconductor for organic devices

Simply alkylated diketopyrrolopyrrole (DPP-C12) (−C12=−C12H25) core has been synthesized and the opto/electrochemical properties are reported. The DPP-C12 can be utilized as a p-channel material in organic devices such as field-effect transistors, resistance load and complementary-type inverters. Both inorganic (OTS-treated SiO2) and polymeric gate insulators were employed in the fabrication of top-contact bottom-gate organic field-effect transistors with DPP-C12 thin-film. Devices are fabricated at different substrate temperatures and the material performance in device was structurally analyzed using atomic force microscope (AFM) and X-ray diffraction (XRD). The DPP-C12 thin-film OFET devices fabricated at Ts=90°C with the polymer gate insulator showed the best performance and the static and dynamic stability was evaluated as a function of time. In addition, the resistance load- and complementary-type inverters using the DPP-C12 thin-film OFET were constructed, and the static and dynamic electrical responses are analyzed in detail.

Voltage-Controlled Ring Oscillators Based on Inkjet Printed Carbon Nanotubes and Zinc Tin Oxide.

A voltage-controlled ring oscillator is implemented with double-gate complementary transistors where both the n- and p-channel semiconductors are deposited by inkjet printing. Top gates added to transistors in conventional ring oscillator circuits control not only threshold voltages of the constituent transistors but also the oscillation frequencies of the ring oscillators. The oscillation frequency increases or decreases linearly with applied top gate potential. The field-effect transistor materials system that yields such linear behavior has not been previously reported. In this work, we demonstrate details of a material system (gate insulator, p- and n-channel semiconductors) that results in very linear frequency changes with control gate potential. Our use of a double layer top dielectric consisting of a combination of solution processed P(VDF-TrFE) and Al2O3 deposited by atomic layer deposition leads to low operating voltages and near-optimal device characteristics from a circuit standpoint. Such functional blocks will enable the realization of printed voltage-controlled oscillator-based analog-to-digital converters.

Synthesis and properties of a new class of fully conjugated azahexacene analogues.

Acenes are a traditional class of polycyclic aromatic hydrocarbons (PAHs) which attracted considerable interest during the last decade because of their outstanding p-channel semiconductor properties. More recently, N-heteroacenes have been prepared. These molecules have been shown to be more stable and can exhibit n-channel semiconductor properties. Inspired by these archetype PAHs, we synthesized a novel class of highly persistent azahexacene analogues 3 a-d. These molecules are composed of a core of four fused five-membered rings derived from their respective diketopyrrolopyrroles. These new π-conjugated scaffolds show broad and intense absorption in the visible region and possess low-lying HOMO and LUMO levels, leading to much better stability compared to that of acenes and most heteroacenes.

Symmetrically functionalized diketopyrrolopyrrole with alkylated thiophene moiety: from synthesis to electronic devices applications

A symmetrically conjugated molecular semiconductor derived from diketopyrrolopyrrole (DPP), i.e., 2,5-dihexadecyl-3,6-bis(5-(3-hexylthiophen-2-yl)thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione [DPP(3HT) 2 ], has been synthesized using the Stille coupling reaction. The optical band gap of DPP(3HT) 2 is found to be 1.65 eV with HOMO energy level of −5.13 eV. DPP(3HT) 2 is thermally stable up to 348 °C exhibiting only 5 % weight loss. X-ray diffraction analysis revealed the DPP(3HT) 2 to be polycrystalline with a high degree of crystallinity. It showed highly narrow and strong diffraction peaks with a d-spacing of ca. 30.18 A (at 2θ = 2.09°, full width at half maximum: 2θ = 0.126°) indicating an end-to-end packing distance with the long alkyl chains (along the a-axis) being slightly tilted and partially interdigitated for effective packing. Field-effect transistors and complementary inverters employing DPP(3HT) 2 as a p-channel semiconductor have been fabricated and characterized.

Thiadiazole dioxide-fused picene: acceptor ability, anion radical formation, and n-type charge transport characteristics

Picene, which is an organic p-channel semiconductor and a component of superconductors, was derivatized with a thiadiazole-dioxide moiety to afford a novel acceptor molecule (PTDAO₂). PTDAO₂ can form stable anion radical species in solution and as a crystal, and its neutral crystalline thin film exhibits n-type transistor characteristics.

Towards solution-processed ambipolar hybrid thin-film transistors based on ZnO nanoparticles and P3HT polymer

Solution-processed n-channel oxide semiconductor thin-film transistors (TFTs) were fabricated using zinc oxide (ZnO) nanoparticles. Polycrystalline fused-ZnO nanoparticle films were produced by spin-coating ZnO nanosphere dispersions following by a subsequent heat treatment. The solution-processable semiconductor ink based on ZnO was prepared by dispersing the synthesized ZnO nanospheres in isopropanol mixed with ethanolamine to various concentrations from 20 to 80mg/mL. Such concentration dependence on morphology and microstructure of thin films was studied on spin-coated ZnO films by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Spin-coated ZnO films involved as active layers in transistor configuration delivered an almost ideal output characteristic (Id–Vd) with an electron mobility up to 3×10−2cm2/Vs. As a p-channel semiconductor, a poly(3-hexylthiophene) (P3HT) solution-processable ink was deposited by spin-coating on top of closely packed ZnO nanoparticles-based films to form an uniform overlying layer. A hybrid (inorganic–organic) interface was formed by the direct contact between ZnO and P3HT leading to carrier redistribution. Such solution-processed hybrid thin-film transistors delivered in air well balanced electron and hole mobilities as 3.9×10−5 and 2×10−5cm2/Vs, respectively.

Non-functionalized soluble diketopyrrolopyrrole: Simplest p-channel core for organic field-effect transistors

We report the synthesis, characterization and behavior in field-effect transistors of non-functionalized soluble diketopyrrolopyrrole (DPP) core with only a solubilizing alkyl chain (i.e. –C16H33 or –C18H37) as the simplest p-channel semiconductor. The characteristics were evaluated by UV–vis and fluorescence spectroscopy, X-ray diffraction, cyclic voltammetry (CV), thermal analysis, atomic force microscopy (AFM) and density functional theory (DFT) calculation. For top-contact field-effect transistors, two types of active layers were prepared either by a solution process (as a 1D-microwire) or thermal vacuum deposition (as a thin-film) on a cross-linked poly(4-vinylphenol) gate dielectric. All the devices showed typical p-channel behavior with dominant hole transports. The device made with 1D-microwiress of DPP-R18 showed field-effect mobility in the saturation region of 1.42×10−2cm2/Vs with ION/IOFF of 1.82×103. These findings suggest that the non-functionalized soluble DPP core itself without any further functionalization could also be used as a p-channel semiconductor for low-cost organic electronic devices.

Perfluoroarene units in distyryl-oligothiophene analogues: An efficient electron density confinement preventing n-type transport in organic thin film transistors

Solid-state properties of two perfluoroarene-containing analogues of distyryl-oligothiophenes (DFSnT, n=2, 4) are presented. High vacuum evaporated thin films were implemented as semiconducting layers into organic thin film transistors (OTFTs). Morphology of thin films has been studied by atomic force microscopy (AFM). OTFT measurements performed under high vacuum show that these compounds behave as only p-channel semiconductors. By using a controlled low evaporation rate together with a fine control of the substrate temperature, highly interconnected μm-long rodlike crystallites were obtained. However, analysis of these materials reveal a direct impact of the molecular structure where the presence of the two double bonds may affect the final transport properties by confining the electrons in such molecular segments and hampering electron delocalization in perfluoroarene units.

New Thienothiadiazole-Based Conjugated Copolymers for Electronics and Optoelectronics

Four new donor–acceptor conjugated copolymers incorporating thieno[3,4-c][1,2,5]thiadiazole as the acceptor moiety and various electron donor moieties were synthesized and their electronic structures and properties were investigated. The new thienothiadiazole copolymers obtained by Stille coupling polymerizations had weight-average molecular weights of 10–46 kDa. Their broad absorption bands and optical band gaps of 0.9–1.2 eV demonstrate strong intramolecular charge transfer and potential for extending light harvesting deep into the near-infrared. The HOMO/LUMO energy levels were 4.9–5.1/3.4–3.6 eV (below vacuum). As p-channel semiconductors in field-effect transistors, the thienothiadiazole copolymers had a carrier mobility of up to 4.6 × 10–3 cm2/(Vs). Bulk heterojunction solar cells made from blends of the thienothiadiazole copolymers with fullerenes gave a photovoltaic efficiency of 0.4%.

A core-extended naphthalene diimide as a p-channel semiconductor

A novel naphthalene diimide with a fully conjugated, extended π-core was synthesized in a one-pot, two-step reaction. This organic semiconductor exhibits ambipolar transport properties with a large hole mobility of 0.56 cm(2) V(-1) s(-1) and a current on/off ratio of 10(6) in bottom-gate, top-contact thin-film transistors prepared by vacuum deposition.

High performance single-crystal field-effect transistors based on twisted polyaromatic semiconductor pyreno[4,5-a]coronene

A novel p-channel semiconductor pyreno[4,5-a]coronene has been synthesized and characterized. The highly fused π-conjugated framework has a twisted geometry with an excellent on-top cofacial π-π stacking in the crystal structure and with a centroid-to-centroid distance of 3.808 Å. Single-crystal field effect transistors based on the molecule exhibit a high mobility of ~0.89 cm(2) V(-1) s(-1) and an on/off ratio of ~6 × 10(4).

Tuning of threshold voltage in organic field-effect transistors with hydrophobic gate dielectric using monoenergetic low-energy electron beams and triode corona

We report organic field-effect transistors (OFETs) with the hydrophobic gate dielectric exposed to an electron beam before semiconductor deposition, shifting the threshold voltage toward positive gate bias for a p-channel semiconductor. A 1 μm Cytop film was irradiated with defined doses of electron beams with different energies. The charges/polarizations embedded in the dielectric by the irradiation have effective charge densities of ∼10−8 C/cm2. OFETs were completed using 5,5′-bis(4-hexylphenyl)-2,2′-bithiophene as the semiconductor, and showed corresponding shifts in Vth. Other OFETs were made where the gate dielectric was treated with a corona discharge. Both types of devices showed similar shifts in Vth and transfer characteristics. There is no change in mobility of the charge carriers after either charging process. The charges do not contribute to the gate capacitance but induce changes in the onset of capacitance increase caused by accumulation of mobile channel charge during capacitance-voltage experiments in two-terminal metal-insulator-semiconductor-metal configurations.

Thiophene–Diazine Molecular Semiconductors: Synthesis, Structural, Electrochemical, Optical, and Electronic Structural Properties; Implementation in Organic Field‐Effect Transistors

The synthesis, structural, electrochemical, optical, and electronic structure properties of a new azine-thiophene semiconductor family are reported and compared to those of analogous oligothiophenes. The new molecules are: 5,5'-bis(6-(thien-2-yl)pyrimid-4-yl)-2,2'-dithiophene (1), 5,5'-bis(6-(5-hexylthien-2-yl)pyrimid-4-yl)-2,2'-dithiophene (3), and 5,5'-bis(6-(thien-2-yl)pyridazin-3-yl))-2,2'-dithiophene (2). Electrochemical experiments demonstrate that introduction of electron-poor heteroaromatic rings into the oligothiophene core significantly enhances electron affinity. Thin-film transistors were fabricated with these materials and evaluated both in vacuum and in air. We find that although diazine substitution is important in tuning oligothiophene orbital energetics, these oligomers are p-channel semiconductors and the field-effect transistor (FET) charge transport properties are remarkably similar to these of unsubstituted oligothiophenes. The combined computational-experimental analysis of the molecular and thin film properties indicates that these diazine-containing oligothiophenes essentially behave as pi-extended bithiophenes. Interestingly, despite strong intermolecular interactions, high solid-state fluorescence efficiencies are observed for these new derivatives. Such emission characteristics suggest that these materials behave as more extended pi systems, which should be advantageous in light-emitting transistors.

Solution Processed Top‐Gate n‐Channel Transistors and Complementary Circuits on Plastics Operating in Ambient Conditions

Top-gate n-TFTs and CMOS circuits on plastic substrates based on solution-processed n- and p-channel semiconductors and polymeric dielectrics have been fabricated. These unencapsulated devices exhibit good performance characteristics in ambient.

Water-stable organic transistors and their application in chemical and biological sensors

The development of low-cost, reliable sensors will rely on devices capable of converting an analyte binding event to an easily read electrical signal. Organic thin-film transistors (OTFTs) are ideal for inexpensive, single-use chemical or biological sensors because of their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. We have fabricated low-operating voltage OTFTs with a cross-linked polymer gate dielectric, which display stable operation under aqueous conditions over >10(4) electrical cycles using the p-channel semiconductor 5,5'-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2'-bithiophene (DDFTTF). OTFT sensors were demonstrated in aqueous solutions with concentrations as low as parts per billion for trinitrobenzene, methylphosphonic acid, cysteine, and glucose. This work demonstrates of reliable OTFT operation in aqueous media, hence opening new possibilities of chemical and biological sensing with OTFTs.

Thin Film Transistors Based on Alkylphenyl Quaterthiophenes: Structure and Electrical Transport Properties

Thin films based on the akylphenyl-substituted quaterthiophenes 5,5‘ ‘‘-bis(4-methylphenyl)-2,2‘:5‘,2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (1), 5,5‘ ‘‘-bis(4-n-propylphenyl)-2,2‘:5‘,2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (2), and 5,5‘ ‘‘-bis(4-hexylphenyl)-2,2‘:5‘,2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (3) were grown by vacuum deposition on thermally grown SiO2 substrates and characterized in a thin film transistor (TFT) configuration. Atomic force microscopy and specular (θ−2θ) X-ray diffraction (XRD) revealed films with small, crystalline grains, in which the oligothiophenes were oriented “end-on” with respect to the SiO2 substrate. Interplanar spacing increased (1 = 28.0 A, 2 = 29.5 A, 3 = 37.7 A), consistent with increasing alkyl tail length. Grazing incidence X-ray diffraction (GIXD) of the films (ca. 350 A thick) revealed nearly equivalent in-plane unit-cell areas (1 = 44.1 A2, 2 = 44.4 A2, 3 = 43.8 A2). The films functioned as p-channel semiconductors in a TFT configuration, exhibiting nearly equivalent hole mobilities...

Linear benzene-fused bis(tetrathiafulvalene) compounds for solution processed organic field-effect transistors

Three new linear benzene-fused bis(tetrathiafulvalene) compounds (4–6) were synthesized and characterized. Compounds 4 and 5, comprising branched alkyl chains (2-ethylbutyl and 2-ethylhexyl, respectively), had very good solubility in common organic solvents and were successfully used as p-channel semiconductors in solution-processed organic field-effect transistors (FET). The FET device based on 5 showed a mobility of 5.6 × 10–4 cm2 V–1 s–1 with an on/off ratio of 1.6 × 104, and the devices based on 4 and 5 displayed good reproducibility in air. In addition, 6, bearing the long n-dodecyl chains, exhibited self-assembly behavior; one-dimensional self-assembly micron-scale ribbons formed in solution and were revealed by scanning electron microscopy on SiO2 substrates.

Flexible Polymer Thin-Film Transistor Device Structures And Processes For 13.56 MHz RF Rectifier Circuits

ABSTRACTPolymeric thin-film transistors (TFTs) have been proposed for several applications including displays, electronic paper, chemical sensors, and radio-frequency identification (RFID) tags. One important technical hurdle that has to be overcome for using organic transistors in RFID tags is for these devices to operate at RF frequencies (typically 13.56 MHz) in the front end. It was long thought that conjugated polymer transistors are too slow for this. In this presentation we will demonstrate that polymer transistor based full-wave rectifier circuits utilizing a polythiophene, a p-channel semiconductor, can operate at this frequency with a useful efficiency. In order to achieve such high-frequency operation, we make use of the non-quasi static (NQS) state of the transistors. Bottom gate and top gate structures are explored and a comparison is made between the observed electrical properties. These circuits are fabricated on PEN (polyethylenenapthalate) or PET (polyethylene-terepthalate) substrates using a spin on dielectric. Gate, source and drain contacts are defined photolithographically using evaporated gold as the metal. Field-effect mobilities in the range of 0.02 and 0.2 cm2/Vs that equal or exceed the highest reported among the ones employing similar geometries on plastic substrates are easily obtained in these systems. In order for NQS based rectification to take place the carrier velocity in a 2 micrometer channel length device needs to be more than 2×104 cm/s. This would correspond to a mobility of 0.1cm2/V-s at a field of 105 V/cm. The rectifiers were based on a 4-transistor full-wave design. A coil (transformer secondary) drives the AC inputs in differential mode. The lower diode connected transistors in a manner similar to the half-wave rectifier define the DC voltage level of the two AC input signals. The two upper transistors are connected as switches and are used to move current from the AC inputs to the positive DC output. The capacitor is used to hold the peak voltage level supplied by the coil through the switch-connected devices. The voltage rectification efficiency is relatively high being as much as 45% at 13.56 MHz. This is among the fastest polymer transistor circuit of any kind demonstrated to date.

Novel highly stable semiconductors based on phenanthrene for organic field-effect transistors

Two novel phenanthrene-based conjugated oligomers were synthesized and used as p-channel semiconductors in field-effect transistors; they exhibit high mobility and excellent stability during long-time ambient storage and under UV irradiation.

Phenoxazine-Based Conjugated Polymers: A New Class of Organic Semiconductors for Field-Effect Transistors

Five new phenoxazine-based conjugated polymers, including poly(10-hexylphenoxazine-3,7-diyl), poly(10-hexylphenoxazine-3,7-diyl-alt-9,9-dihexyl-2,7-fluorene), and poly(10-hexylphenoxazine-3,7-diyl-alt-3-hexyl-2,5-thiophene), were synthesized, characterized, and successfully used as p-channel semiconductors in organic field-effect transistors. The polymers have high glass transition temperatures in the 112−230 °C range. The phenoxazine-based polymers have low ionization potentials or high-lying HOMO levels (4.8−4.9 eV), which were estimated from cyclic voltammetry. Organic field-effect transistors based on the phenoxazine polymer semiconductors have a field effect hole mobility of up to 6 × 10-4 cm2/(V s) and an on/off ratio of up to 104. These results demonstrate that phenoxazine-based conjugated polymers are promising p-type semiconductors for solution processable thin film transistors.