Organic Single-crystal Transistors Research Articles

Highly sensitive detecting system to precisely evaluate the emission spectra and quantum efficiency of organic crystal light-emitting transistors.

The lack of a reliable and sensitive measure system has strongly hindered the progress of organic single-crystal light-emitting transistors, since their emission spectra and absolute intensity were rather difficult to be measured as a consequence of small area and weak emission, as well as their edge emission feature. Hence, a tailor-made detecting system was set up by combining a semiconductor analyzer and a rotatable microscope coupling with a highly sensitive grating spectrometer. The detecting system solved the important issue of quantitatively characterizing the optoelectronic properties of organic transistors, especially those based on single crystals. With organic lamellar single crystals, we confirmed that the measurement system was reliable and had enough sensitivity to precisely evaluate the performance of light-emitting transistors corresponding to the emission spectra.

Measuring the impact of spin-triplet exciton orientation on photocurrent in an organic transistor

Angle dependent magneto-photocurrent in organic single crystal transistors reveals the anisotropy of triplets, verified by a spin-Hamiltonian model with zero-field splitting, providing a basis for metrics of singlet fission–triplet fusion devices.

Short Alkyl Chain Engineering Modulation on Naphthalene Flanked Diketopyrrolopyrrole toward High‐Performance Single Crystal Transistors and Organic Thin Film Displays

AbstractStudying multi‐purpose applications of a specific material is a challenging topic in the organic electronics community. In this work, through molecular engineering and smart device structure design strategy, high performance in transistors and thin film display devices is simultaneously achieved by applying a simple new dye molecule, naphthalene flanked diketopyrrolopyrrole (DPPN), as the active layer material. Short alkyl chains (hexyl or octyl side groups for H‐DPPN and O‐DPPN, respectively) are adapted to improve the hole mobility in organic thin film transistors (OTFTs) and single crystal transistors (SCTs). Specifically, H‐DPPN shows a similar hole mobility in either OTFTs or SCTs, while O‐DPPN exhibits a dramatically enhanced mobility, reaching 0.125 cm2 V−1 s−1 in SCTs. Additionally, a smart organic light emitting diode (OLED) device is designed by using DPPN molecule as the dopant with a host matrix. The promising external quantum efficiencies of 4.0% and 2.3% are achieved for H‐DPPN and O‐DPPN fabricated OLEDs. Overall, in this work, it is reported that DPP‐based small molecules can simultaneously function well in both transistors and thin film displays with high device performance through molecular and smart device engineering.

Low-voltage complementary inverters using solution-processed, high-mobility organic single-crystal transistors fabricated by polymer-blend printing

Organic field-effect transistors (OFETs) have attracted great attention as key elements in Internet-of-Thing (IoT) devices due to their advantages of low cost and mass producibility made possible by printing technology. Such devices require organic semiconductors (OSCs) that intrinsically possess high carrier mobility and air stability. In addition, the demand for low-voltage operation and low power consumption has been increasing because the potential power sources for actual devices are implementable energy harvesters that supply low power and low voltages. Based on recently developed high-performance single-crystal p-type and n-type OSCs, this work demonstrated air-stable, high-mobility OFETs with low-voltage operation by using an insulating polymer-blend printing method. By comparing two acrylic polymers poly(methyl methacrylate) and poly(adamantyl methacrylate) (PADMA), having remarkably different thermal properties, we found that PADMA showing a high glass transition temperature >200 °C was suitable for device fabrication, enhancing the flexibility of OSC materials. Also, PADMA spontaneously produced good charge-transport interfaces with the OSC single crystals, leading to high carrier mobilities of 6.6 and 2.2 cm2 V−1 s−1 in p-channel and n-channel OFETs at ≤1.5 V, respectively. The current electron mobility was the highest among low voltage-operation OFETs reported so far. These high-mobility OFETs were integrated into a complementary inverter, for which a low static power consumption of 6.6 pW was confirmed. Therefore, this study reports an advantage of polymer-blend printing for OFETs with enhanced processability and performance suitable for IoT applications.

Organic Single-Crystal Transistor with Unique Photo Responses and Its Application as Light-Stimulated Synaptic Devices.

Tremendous progress has been achieved on organic transistor-based photodetectors; however, because of the nonpositive correlation relationship between the photo/dark current ratio (P) and the gate voltage, the claimed best P, R (photoresponsivity), and D* (detectivity) can hardly be obtained simultaneously at a given gate voltage, which severely compromises the device performance. Here, a light and voltage dually gated transistor based on an organic semiconducting single crystal of 2,6-dithienylanthracene (DTAnt) is developed. Attributing to its very low on/off ratio in the dark and the remarkable increment of mobilities under illumination, this phototransistor shows good performance with a P of 3.83 × 103, R of 1.32 A W-1, and D* of 1.94 × 1012 Jones achieved simultaneously at Vg = -100 V. Besides, the good reversibility and repeatability of its light-responsive behavior allows for the construction of an artificial photonic neuromorphic device with demonstrated synaptic functions, including excitatory postsynaptic current, short/long-term memory , and pair-pulse facilitation/depression.

Enhanced ambipolar charge transport for efficient organic single crystal light-emitting transistors with a narrowed ambipolar regime

An efficient ambipolar OLET was constructed based on a high-mobility emissive 2,6-diphenylanthracene semiconductor via energy-level engineering, giving a narrowed ambipolar regime with strong light emission.

Exfoliated Graphite Electrodes for Organic Single-Crystal Field-Effect Transistor Devices

In this work, exfoliated graphite was used as an electrode for organic single-crystal field-effect transistor (FET) devices, and the electrode performance was demonstrated. The reduced rigidity of ...

Photolithography-Compatible Flexible Electrodes Conformed Onto an Organic Bulk Crystal for Fabrication of Large-Scale Organic Transistor Array

Based on a pre-grown rubrene bulk crystal, a large-scale rubrene single-crystal transistor array is fabricated with photolithography-compatible flexible electrodes on bulk crystal. The resulting organic single-crystal transistor array exhibits a high yield with 100% device operation. The average mobility in an array with an area of $560\,\,\mu \text{m}\,\,\times 400\,\,\mu \text{m}$ is 13.8 ± 5.9 ${\mathrm {cm}}^{\textsf {2}}/\text{V}\cdot \text{s}$ , the highest mobility obtained is 25.1 ${\mathrm {cm}}^{\textsf {2}}/\text{V}\cdot \text{s}$ , and the current ON/OFF ratio can reach $7.2\,\,\times \,\, 10^{\textsf {5}}$ . These results offer a novel approach for obtaining high-integration, high-precision organic single-crystal device arrays. It also enables an effective method to study the intrinsic properties and circuit design based on an organic crystal.

Remarkably low flicker noise in solution-processed organic single crystal transistors

Low-frequency noise generated by a fluctuation of current is a key issue for integrating electronic elements into a high-density circuit. Investigation of the noise in organic field-effect transistors is now sharing the spotlight with development of printed integrated circuits. The recent improvement of field-effect mobility (up to 15 cm2 V−1 s−1) has allowed for organic integrated circuits with a relatively high-speed operation (~50 kHz). Therefore, an in-depth understanding of the noise feature will be indispensable to further improve the circuit stability and durability. Here we performed noise measurements in solution-processed organic single crystal transistors, and discovered that a low trap density-of-states due to the absence of structural disorder in combination with coherent band-like transport gives rise to an unprecedentedly low flicker noise. The excellent noise property in organic single crystals will allow their potential to be fully exploited for high-speed communication and sensing applications.

Photolithography-compatible conformal electrodes for high-performance bottom-contact organic single-crystal transistors

A novel photolithography-compatible conformal electrode was demonstrated for the fabrication of high-performance bottom-contact organic single-crystal transistors on planar and curved surfaces.

Photochemical Molecular Tailoring for Efficient Diffusion and Reorganization of Organic Nanocrystals for Ultra-Flexible Organic Semiconductor Arrays.

Solution-processed organic single crystals with high carrier mobility have been actively investigated for diverse applications such as displays, sensors, and next generation electronics on a flexible platform. However, the lack of precise alignment and growth control of organic single crystals impedes the widespread adoption of organic materials in an industrial perspective. Here, a photochemical modification approach is reported tailoring the solubility and molecular diffusivity of polymeric sacrificial layer and sequential batch-type vapor annealing to implement high-performance (average saturation mobility: 8.01 cm2 V-1 s-1 ) organic single-crystal thin film transistors with large channel width including multiple aligned single crystals. Additionally, the mechanical properties of the organic single crystals are systematically investigated with extreme strain conditions such as bending radius of 150 μm.

Controllably Aligned Ultra-Flexible and High-Performance Organic Single-Crystal Arrays Via Solvent Vapor Annealing for Large Area Soft Electronics

Recently, semiconducting organic materials have been actively investigated for achieving high performance organic thin-film transistors and applying to diverse electronic applications. Particu-larly, in order to control the location and direction of organic single crystals with a densely packed molecular structure, several techniques such as inkjet printing and sheared deposition us-ing a self-assembled mono-layer pattern have been suggested. In this presentation, we used sol-vent vapor anneal (SVA) process of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic films, forming diverse patterns of their organic single crystals. Room-temperature photochemical patterning of polymer dielectric layer by using deep ultraviolet (DUV) enables the determined organization of C8-BTBBT single crystals with controlled-position and orientation. In SMSVA process, C8-BTBT small molecules become mobile on soluble polymer layer and re-assembled into micro rod-shaped single crystal only at pristine polymer dielectric region. Using the novel SVA, C8-BTBT single crystal arrays were easily produced on narrow trench of pristine polymer dielectric while their diverse patterns such as a multi-lines, zigzags and star shape were readily possible as well. Based on these arrays of C8-BTBT single crystals, we fabricated high performance and large current organic single crystal transistor on a 3-μm-thick flexible film in which the saturation mobility of devices exceeds ~ 3 cm2 V-1s-1 for one single crystal micro-rod. It was also found that the high performance of single crystal transistor remained functional following the aggressive bending test. We rolled up the device on optical fiber (bending radius:150 μm). After the bending test, the devices show reliable performance without significant degradation from its initial characteristics.

Controllably Aligned Ultra-Flexible and High-Performance Organic Single-Crystal Arrays Via Solvent Vapor Annealing for Large Area Soft Electronics

We used deep ultraviolet (DUV) irradiation onto polymeric sacrificial layer of PMMA for micro-rod single crystallization of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) with the controlled location and orientation in the subsequent process of solvent vapor annealing (SVA) process. We fabricated ultra-flexible organic single crystal transistors, showing mechanical flexibility with bending radius of 150μm on optical fiber. After the bending test, the devices show reliable performance without significant degradation from its initial characteristics.

Organic Single-Crystal Transistors Based on DBT3 Derivatives

Heteroacenes that contain chalcogenophene have been actively investigated as semiconducting materials because they are more stable in air than acenes and various chemical modifications of the compounds are possible. While there have been many attempts to combine benzene with thiophene rings to produce higher-performance materials, only a few derivatives are known to show high mobilities above 1 cm2 /Vs. Also OFETs of high performance have been often achieved by using expanded heteroaromatic of π-conjugated including thiophene oligomers as the semiconducting materials. In this work, we synthesize new type of fused chalcogenophene based transistor materials, 54DBTTT and 8-67DBTTT (Fig. 1), and investigate the characterization of organic single-crystal transistors based on the newly developed materials. We made organic single crystals of 54DBTTT and 8-67DBTTT by physical vapor transport (PVT) and drop-cast method. We used an n +-doped Si wafer with 220 nm thickness thermally grown SiO2, which was covered with a thin film (ca. 27.8 nm) of CYTOP insulator or a thin film (ca. 30 nm) of poly(methyl methacrylate) (PMMA) insulator. Source and drain electrodes were painted with a colloidal graphite paste. The field-effect mobility (μ) of the OFET devices were measured under vacuum from the saturation regime according to the equation: I d=μC i(W/2L)(V g-V th)2, where C i is capacitance of the insulator, V d and V th are the gate and threshold voltages, respectively. To investigate the molecular conformation and stacking of the molecules in the crystal states, single-crystal X-ray analysis was performed. In contrast to the herringbone structure 54DBTTT, 8-67DBTTT molecules exhibit a two-dimensional brick-wall packing arrangement (Fig. 2). Organic single-crystal transistors based on DBTTT derivatives showed typical p-channel FET characteristic. The best field-effect mobility of 0.3 cm2 /Vs was obtained for 54DBTTT based single-crystal device with a CYTOP covered Si/SiO2 substrate. On the other hand, the mobility for the 8-67DBTTT based transistor was 8.1x10-3 cm2 /Vs. As shown above, molecular packing structure of the 8-67DBTTT is brick-wall packing. Acoording to the Fig. 2(d) alkyl chain placed between the DBTTT cores, which is not preferable to the high performance OFET device. Figure 1

Highly sensitive H2S sensors based on ultrathin organic single-crystal microplate transistors

Based on ultrathin dinaphtho[3,4-d:3′,4′-d′]benzo[1,2-b:4,5-b′]dithiophene (Ph5T2) single-crystal microplates, the highly sensitive organic field-effect H2S sensors are realized at room temperature. The response is as high as 1.2 × 106% in 50 ppm H2S. This value is extremely high for H2S sensors, and is three orders of magnitude higher than that of the most reported semiconductor gas sensors. The response/recovery time is respectively as low as 2 min and 1 min in 50 ppm H2S. The detect limitation is as low as 0.5 ppm. The ultrathin single-crystal microplates provide direct and efficient ways for the analytes' activities within the conducting channel, and therefore mainly account for the improved sensing performance. The excellent sensing performance of ultrathin Ph5T2 single-crystal microplate transistors reveals the capacity of developing highly sensitive room-temperature sensors.

Organic Single-Crystal Nanowire Transistor Fabricated by Glass Fiber Mask Method

The commercialized, low-cost, and lightweight glass fiber microwires have been shown as a new mask to simplify the fabrication of organic single-crystal nanowire transistors based on copper phthalocyanine (CuPc). The glass fiber is light weight so that the van der Waals force is capable of resisting the effect of gravity when the substrate is flipped over. In this case, the glass fiber mask need not be artificially fixed onto the substrate during metal deposition for electrode fabrication, so the device fabrication process can be simplified. With such a facile method, multiple organic single-crystal nanowire transistors can be fabricated at the same time, and the high mobility up to 0.7 cm $^{2}\text{V}^{{-1}}\text{s}^{{-1}}$ has been realized for CuPc nanowire transistors. Good stability has been also demonstrated. This method effectively improves the efficiency of devices preparation, showing the potential in large-scale fabrication of organic nanowire transistors. Meanwhile, it is favorable for the fundamental electrical studies of 1-D organic nanomaterials.

Organic single-crystal transistors and circuits on ultra-fine Au wires with diameters as small as 15 μm via jigsaw puzzle method

A novel jigsaw puzzle method was developed to fabricate the high-performance CuPc and F16CuPc organic single-crystal field-effect transistors and circuits on ultra-fine and flexible Au wires with diameters as small as $15~\mu \text{m}$ . This method weakens the effect of fiber size on the device-fabrication process and provides a simple way to realize organic single-crystal complementary circuits on ultra-fine fibers. The resulting high-performance miniaturized fiber-shaped devices with extremely small diameters have strong potential for the applications in wearable and implantable electronics.

Applications of parylene films in the manufacture of organic field-effect transistors

Abstract Along with the technology of microscopic electromechanical systems and that of brain–machine interface, the area of organic electronics presents a major development direction of high-tech applications of parylene coatings. Within this area, a fabrication of organic field-effect transistors (OFETs), where parylene C is applied as a gate dielectric, makes the most common use of these materials. The main advantage of parylene coatings in the OFET technology is their very high purity. Depending on a transistor design, films of parylene C may play a role of the gate dielectric material, that of a protective insulator coating, and/or that of a device substrate. The work presents a number of applications of parylene C in different OFET devices, namely in organic thin film transistors (OTFTs) and organic single-crystal transistors developed by the authors. A combination of zone-cast films of active materials, both n-type and p-type, with parylene C gate dielectric makes a principal design of the OTFTs. In this group, the best performance parameters and namely μFE = 0.18 cm2/Vs, Ion/off = 104 and turn-on voltage

High‐Performance UV‐Sensitive Organic Phototransistors Based on Benzo[1,2‐b:4,5‐b′]dithiophene Dimers Linked with Unsaturated Bonds

Obvious differentiated response of organic phototransistors (OPTs) to the lights with different wavelengths is a challenge but a prerequisite for wavelength‐selective applications. In this manuscript, highly UV‐sensitive OPTs are fabricated based on benzo[1,2‐b:4,5‐b′]dithiophene dimers (BBDT, BBDTE, and BBDTY). The BBDTE‐based organic single‐crystal transistors (OSCTs), which show carrier mobility up to 1.62 cm2 V−1 s−1, exhibit a maximum photoresponsivity up to 9821 A W−1 and a maximum photosensitivity up to 105 towards UV light (37 μW cm−2), and the photosensitivity observed within tested light intensity range is unexpectedly stable. The BBDTY‐based OPTs also exhibit differentiated response between UV and visible lights, even with thin‐film state of organic semiconductor, and the highest photoresponsivity and photosensitivity to UV light reached 9336 A W−1 and 4429, respectively. This selective and highly sensitive performance enables unsaturated bond‐linked benzo[1,2‐b:4,5‐b′]dithiophene dimers promising candidates for UV detectors.

Ambipolar light-emitting organic single-crystal transistors with a grating resonator.

Electrically driven organic lasers are among the best lasing devices due to their rich variety of emission colors as well as other advantages, including printability, flexibility, and stretchability. However, electrically driven lasing in organic materials has not yet been demonstrated because of serious luminescent efficiency roll-off under high current density. Recently, we found that the organic ambipolar single-crystal transistor is an excellent candidate for lasing devices because it exhibits less efficient roll-off, high current density, and high luminescent efficiency. Although a single-mode resonator combined with light-emitting transistors (LETs) is necessary for electrically driven lasing devices, the fragility of organic crystals has strictly limited the fabrication of resonators, and LETs with optical cavities have never been fabricated until now. To achieve this goal, we improved the soft ultraviolet-nanoimprint lithography method and demonstrated electroluminescence from a single-crystal LET with a grating resonator, which is a crucial milestone for future organic lasers.