Organic Single-crystal Devices Research Articles

Controlled growth of organic single-crystal arrays on hydrophobic substrate surface for high-performance transistors

<p indent="0mm">Optoelectronic devices such as organic field-effect transistors (OFETs) and organic light-emitting diodes are expected to achieve low-cost flexible optoelectronic applications, but the low-cost potential depends on the capability of large-area deposition of organic semiconducting single-crystal (OSSC) arrays based on solution methods. However, poor surface-wetting behavior and sophisticated fluid kinetics limit solution deposition of large-scale OSSC arrays. Herein, the wetting-ability and fluid drying dynamics were improved by adding trace surfactants, and the affinity between organic solution and hydrophobic surface was also enhanced. In addition, the groove structures of polydimethylsiloxane templates were used as confined spaces for the nucleation, crystallization, and growth of OSSCs, and finally an OSSC array over large areas was prepared. This strategy has good universality for materials and patterns. OFETs based on the OSSC array show good performance and uniformity. These illustrations will provide more opportunities for integrated applications of organic single-crystal devices.

Water permeation pathways in laminated organic single-crystal devices

Water permeation pathways in electronic devices should be eliminated for the suppression of operational instabilities. We investigated possible pathways in field-effect transistors based on a laminated single crystal (SC) of an organic semiconductor, rubrene. Water-induced instabilities were found to be more obvious with a thicker rubrene SC. Furthermore, under our simulation conditions, molecular dynamics calculations of water diffusion on a rubrene SC showed that no water molecules penetrated the SC. These findings indicate that a space at the SC/substrate interface is a dominant pathway. The present study clearly shows the importance of conformality of SC lamination onto the underlying substrate.

Flexible Organic Single-Crystal Field-Effect Transistor for Ultra-Sensitivity Strain Sensing

To date, the functional application of the flexible organic single-crystal devices in strain sensors has not been studied. In this letter, the excellent flexibility of the beltlike rubrene single crystals enables the rubrene single-crystal field-effect transistors to be bent inward and outward, and their electrical properties under compressive and tensile strain are demonstrated. The current and mobility of the device show the nearly linear changes under the tensile and compressive strain of <0.4%. The dynamic response of the strain presents good repeatability. The calculated sensitivity under tensile strain is two orders of magnitude higher than the previously reported organic thin-film-based strain sensor. It is demonstrated that the rubrene single-crystal device can effectively detect the movement of a human finger. These results exhibit the promising potential of our transistors in artificial intelligence and healthcare systems.

Solution-printed organic semiconductor blends exhibiting transport properties on par with single crystals.

Solution-printed organic semiconductors have emerged in recent years as promising contenders for roll-to-roll manufacturing of electronic and optoelectronic circuits. The stringent performance requirements for organic thin-film transistors (OTFTs) in terms of carrier mobility, switching speed, turn-on voltage and uniformity over large areas require performance currently achieved by organic single-crystal devices, but these suffer from scale-up challenges. Here we present a new method based on blade coating of a blend of conjugated small molecules and amorphous insulating polymers to produce OTFTs with consistently excellent performance characteristics (carrier mobility as high as 6.7 cm2 V−1 s−1, low threshold voltages of<1 V and low subthreshold swings <0.5 V dec−1). Our findings demonstrate that careful control over phase separation and crystallization can yield solution-printed polycrystalline organic semiconductor films with transport properties and other figures of merit on par with their single-crystal counterparts.

A high-yield two-step transfer printing method for large-scale fabrication of organic single-crystal devices on arbitrary substrates.

Single-crystal organic nanostructures show promising applications in flexible and stretchable electronics, while their applications are impeded by the large incompatibility with the well-developed photolithography techniques. Here we report a novel two-step transfer printing (TTP) method for the construction of organic nanowires (NWs) based devices onto arbitrary substrates. Copper phthalocyanine (CuPc) NWs are first transfer-printed from the growth substrate to the desired receiver substrate by contact-printing (CP) method, and then electrode arrays are transfer-printed onto the resulting receiver substrate by etching-assisted transfer printing (ETP) method. By utilizing a thin copper (Cu) layer as sacrificial layer, microelectrodes fabricated on it via photolithography could be readily transferred to diverse conventional or non-conventional substrates that are not easily accessible before with a high transfer yield of near 100%. The ETP method also exhibits an extremely high flexibility; various electrodes such as Au, Ti, and Al etc. can be transferred, and almost all types of organic devices, such as resistors, Schottky diodes, and field-effect transistors (FETs), can be constructed on planar or complex curvilinear substrates. Significantly, these devices can function properly and exhibit closed or even superior performance than the device counterparts fabricated by conventional approach.

Organic single crystals: Addressing the fundamentals of organic electronics

Abstract

Anisotropy in Organic Single‐Crystal Photovoltaic Characteristics

Organic single crystals have been well researched for many years. Typical vapor-phase growth of organic crystals developed from vertical to horizontal growth in order to achieve improved crystalline quality. Recently, a field-effect study on these single-crystal semiconductors demonstrated high carrier mobilities, up to ca. 15 cm Vs, along with anisotropic charge-transport properties. These single-crystal transistors were usually fabricated with rigid and thick crystals (tens of micrometers to millimeters), which were fragile and difficult to process because of poor mechanical properties. Recently, a growth method affording thin, 150 nm thick, organic crystals demonstrated the processability of single-crystal transistors on flexible substrates, and these organic crystals could be patterned on individual channels for transistors. However, in addition to transistor studies of these organic crystals, other types of electronic applications, such as two-terminal devices, have not yet been realized, mainly because of the difficultly processing thick crystals. In this Communication, we report organic single-crystal photovoltaics fabricated from single pieces of thin tetracene crystals on bilayer heterojunctions with fullerene (C60) thin films. These organic singlecrystal devices exhibited excellent diode behavior with rectifying ratios of 10 and an external power conversion efficiency (PCE) of ca. 0.34 %. By employing these high-quality single crystals in two-terminal devices, high-performance optoelectronic devices, such as organic diodes, photovoltaics, and photodetectors, become possible alternatives for large-area, low-cost flexible electronics. The quality of the single crystals was examined by cross-polarized microscopy, X-ray powder diffraction (XRD), and single-crystal X-ray diffraction. The optical microscopy images (Fig. 1a and b) recorded at 0° and 90° from the entrance polarizer and exit analyzer, respectively, show large birefringence, confirming the anisotropic crystalline nature of the tetracene crystals. The XRD data exhibit strong and narrow first (001) and second order (002) reflections (Fig. 1c), indicating the tetracene crystal is c-oriented, with molecular-plane growth along the vertical direction. The crystal data obtained for tetracene confirm a C18H6 molecular formula with a molecule weight of 222.23 g mol. The lattice constants are a = 6.02 ± 0.025 A, b = 7.77 ± 0.032 A, c = 12.46 ± 0.054 A, a =101.11 ± 0.078°, b = 99.41 ± 0.092°, and c = 94.40 ± 0.088°, and tetracene crystallizes with a triclinic crystal structure in space group P 1. The coordinates for tetracene can be obtained in the crystallographic information file (CIF) format from the Cambridge Crystallographic Data Center (CCDC), and the above crystallographic data are consistent with the data in the CCDC. Both the strong birefringence and the XRD results indicate these organic single crystals are of high quality. A schematic structure of a single-crystal solar cell is shown in Figure 2a. The device structure comprised a poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS)coated indium tin oxide (ITO) substrate, a tetracene crystal, evaporated thin films of C60 and bathocuproine (BCP), and an aluminum thin-film electrode. We note that thin crystals (ca. 200 nm) used in this study conformed better on substrates C O M M U N IC A IO N

In Situ Patterning of Organic Single‐Crystalline Nanoribbons on a SiO2 Surface for the Fabrication of Various Architectures and High‐Quality Transistors

Organic single-crystalline nanoribbons are fabricated through an in situ patterning technique to yield various architectures. Organic field-effect transistors based on such patterned nanoribbons (see figure) are shown to exhibit low threshold voltages and high carrier mobilities. This in situ patterning technique overcomes the general disadvantages of the handpicking process for the fabrication of organic single-crystal devices and opens up a new route for the fabrication of architectures and devices using nanocrystals.

High-Performance Air-Stable n-Type Transistors with an Asymmetrical Device Configuration Based on Organic Single-Crystalline Submicrometer/Nanometer Ribbons

High-performance air-stable n-type field-effect transistors based on single-crystalline submicro- and nanometer ribbons of copper hexadecafluorophthalocyanine (F(16)CuPc) were studied by using a novel device configuration. These submicro- and nanometer ribbons were synthesized by a physical vapor transport technique and characterized by the powder X-ray diffraction pattern and selected area electron diffraction pattern of transmission electron microscopy. They were found to crystallize in a structure different from that of copper phthalocyanine. These single-crystalline submicro- and nanometer ribbons could be in situ grown along the surface of Si/SiO(2) substrates during synthesis. The intimate contact between the crystal and the insulator surface generated by the "in situ growing process" was free from the general disadvantages of the handpicking process for the fabrication of organic single-crystal devices. High performance was observed in devices with an asymmetrical drain/source (Au/Ag) electrode configuration because in such devices a stepwise energy level between the electrodes and the lowest unoccupied molecular orbital of F(16)CuPc was built, which was beneficial to electron injection and transport. The field-effect mobility of such devices was calculated to be approximately 0.2 cm(2) V(-)(1) s(-)(1) with the on/off ratio at approximately 6 x 10(4). The performances of the transistors were air stable and highly reproducible.