TIPS-pentacene Crystals Research Articles

Tuning charge transport in organic semiconductors with nanoparticles and hexamethyldisilazane

In this study, we showcase the use of silicon dioxide (SiO2) nanoparticles and hexamethyldisilazane (HMDS) treatment to regulate the thin film morphology and manipulate charge transport of solution-processed, small-molecular, organic semiconductors. 6,13-Bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was blended with SiO2 nanoparticles as an exemplary organic semiconductor. A higher concentration of SiO2 nanoparticles were observed near the edge of TIPS pentacene crystals and enlarged the width of crystal edges. This greatly reduced the dendritic crystal growth pattern of TIPS pentacene and contributed to its enhanced orientation uniformity. In addition, the HMDS treatment effectively passivated the silanol groups on the hydrophilic gate dielectrics. As a result, bottom-gate, top-contact TIPS pentacene/SiO2 nanoparticle-based organic thin-film transistors boosted a performance consistency enhancement (defined by the ratio of average mobility to the standard deviation of mobility). The combinational approach to employ SiO2 nanoparticles and HMDS treatment as demonstrated in this work sheds light on important applications in high-performance organic electronics devices on flexible substrate.

Poly(α-methylstyrene) polymer and small-molecule semiconductor blend with reduced crystal misorientation for organic thin film transistors

The electrical performance of solution-processed, small-molecule organic semiconductors is largely restricted by their severe charge carrier mobility variations. In this work, we demonstrate an effective method to reduce such variations of the semiconductor mobilities and improve the performance consistency of organic thin film transistors (OTFTs) by adding poly(α-methylstyrene) (PαMS) as a polymer additive. By using 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) as an example, we found that while pristine TIPS pentacene film exhibited random crystal orientation and large film gaps, the addition of PαMS polymer promoted the growth of semiconductor crystals, which formed uniformly aligned needles with significantly improved orientation and coverage within the channel regions. An ultra-low misorientation angle of 2.2° ± 1° was obtained from TIPS pentacene/PαMS blend film, which is a 20-fold reduction as compared to pristine TIPS pentacene. Bottom-gate, top-contact OTFTs with TIPS pentacene crystals aligned perpendicularly from source to drain contact electrodes demonstrated a hole mobility of up to 0.26 cm2/V s, as well a 6-fold enhancement of average mobility as compared to the pristine TIPS pentacene based counterparts. Notably, the addition of PαMS led to a performance consistency factor of 3.35, as defined by the ratio of the average mobility to standard deviation, implying a great reduction of charge carrier mobility variations. The improvement of electrical performance of OTFTs can be attributed to the combined outcome of crystal rigid alignment, extended long-range order, and almost full coverage of charge transport channel.

Correlation between surface morphology and potential profile in OFETs with zone-cast TIPS-Pentacene as seen by scanning Kelvin probe microscopy

Abstract Charge-carrier transport in the channel of bottom gate, top contact organic field effect transistors with anisotropic layers of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pentacene) obtained by zone casting was investigated using scanning Kelvin probe microscopy combined with atomic force microscopy. The TIPS-Pentacene continuous layers consisted of thin crystals unidirectionally oriented in the channel. Devices with perpendicular and parallel charge flow in the transistor channel were prepared. It was found that irregularities in the surface morphology at the semiconductor layer in the transistor channel are correlated with the local potential profile, and that the channel resistance strongly depends on the orientation of the TIPS-Pentacene crystals.

Self-assembly crystal microribbons with nucleation additive for high-performance organic thin film transistors

We demonstrate fabrication of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) crystal microribbon based organic thin film transistors (OTFTs) with a solvent exchange method and the addition of a nucleation agent. TIPS pentacene crystals were formed via self-assembly as a result of solubility difference between the double solvents. At the same time, 4-hexylbenzoic acid (HBA) was added as a nucleation agent and formed an interfacial layer on the silicon dioxide gate dielectrics, which dispersed the aggregated crystals and enhanced its morphology uniformity. TIPS pentacene crystal microribbon based OTFTs with HBA nucleation additive showed a hole mobility of up to 0.36 cm2 V−1 s−1, and particularly, a 9-fold enhancement in average mobilities, as compared to pristine crystal based OTFTs. The remarkable enhancement in device performance can be attributed to the improved crystallinity, reduced defects and charge trap centers located at the grain boundaries, and controlled crystallization and dispersion effect due to the addition of the HBA nucleation agent.

Effect of lateral confinement on crystallization behavior of a small-molecule semiconductor during capillary force lithography for use in high-performance OFETs

In the current work, we carry out an analysis on micro-patterned 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) crystals grown by capillary force lithography (CFL) to investigate the effect of lateral confinement on the crystallization. From systematic analysis on the crystal orientation and crystallinity depending on the line widths of the crystal patterns, it is revealed that crystals grown from highly confined conditions, namely from patterns with line widths of 5 μm, are observed to be more uniaxially aligned, have much fewer grain boundaries, and yield better field-effect mobility (μFET) as high as 1.66 cm2/(V s) in organic field-effect transistors (OFETs) compared to the wider line widths. These results demonstrate that the lateral confinement during CFL is able to promote the growth of well-aligned TIPS-pentacene crystals with high crystallinity. Thus, we expect our systematic work with CFL, a type of soft lithography, could provide insight for OFETs to step toward their integration in commercial devices.

TIPS-pentacene/Copper (II) phthalocyanine bi-layer photo sensitive organic field-effect transistors

In this work, a combination of a thin layer of Copper (II) phthalocyanine (CuPc) and TIPS-pentacene crystal was used to enhance the photo-sensing spectrum of photo- sensitive organic field-effect transistors (photo-OFETs). In TIPS-pentacene/CuPc bi-layer devices, the different conduction path not only reduced the total number of traps but also enhanced the sensing spectrum. It was found that, though the TIPS-pentacene was able to sense only blue and green colour well, and CuPc was able to sense only red and green colour well; the TIPS-pentacene/CuPc bi-layer were able to sense all three colors, enhancing the range of sensing. On illumination, bi-layer TIPS-pentacene/CuPc OFETs exhibited higher values of shift in threshold voltage (|ΔVTH|) compared to neat TIPS-pentacene and bare CuPc OFETs, due to change in the spatial distribution in the trap state density and associated pattern of trapping of photo-generated charge carriers. It was also found that the values of photo-responsivity (Rmax) and photo-detection time for the bi-layer OFETs were in between that for OFETs with TIPS-pentacene or CuPc.

Effect of Crystallization Modes in TIPS-pentacene/Insulating Polymer Blends on the Gas Sensing Properties of Organic Field-Effect Transistors

Blending organic semiconductors with insulating polymers has been known to be an effective way to overcome the disadvantages of single-component organic semiconductors for high-performance organic field-effect transistors (OFETs). We show that when a solution processable organic semiconductor (6,13-bis(triisopropylsilylethynyl)pentacene, TIPS-pentacene) is blended with an insulating polymer (PS), morphological and structural characteristics of the blend films could be significantly influenced by the processing conditions like the spin coating time. Although vertical phase-separated structures (TIPS-pentacene-top/PS-bottom) were formed on the substrate regardless of the spin coating time, the spin time governed the growth mode of the TIPS-pentacene molecules that phase-separated and crystallized on the insulating polymer. Excess residual solvent in samples spun for a short duration induces a convective flow in the drying droplet, thereby leading to one-dimensional (1D) growth mode of TIPS-pentacene crystals. In contrast, after an appropriate spin-coating time, an optimum amount of the residual solvent in the film led to two-dimensional (2D) growth mode of TIPS-pentacene crystals. The 2D spherulites of TIPS-pentacene are extremely advantageous for improving the field-effect mobility of FETs compared to needle-like 1D structures, because of the high surface coverage of crystals with a unique continuous film structure. In addition, the porous structure observed in the 2D crystalline film allows gas molecules to easily penetrate into the channel region, thereby improving the gas sensing properties.

Orientation Control of Solution-Processed Organic Semiconductor Crystals To Improve Out-of-Plane Charge Mobility

The crystallization of a series of triisopropylsilylethynyl (TIPS)-derivatized acene-based organic semiconductors drop cast from solution onto substrates was investigated as a function of the size of their conjugated cores. When drop cast onto a substrate, the molecules in TIPS-pentacene crystals adopt a “horizontal” orientation, with the long axis of the pentacene core parallel to the substrate surface. For crystals comprising molecules with dibenzopyrene, anthanthrene, and pyranthrene cores, two-dimensional X-ray diffraction patterns revealed the existence of a second population of crystals adopting a “vertical” molecular orientation with the long axis of the acene core perpendicular to the substrate surface. The ratio of the population of TIPS-pyranthrene crystals with molecules adopting horizontal versus vertical orientations was controlled by varying the surface energy of the underlying substrate. These crystals displayed orientation-dependent linear birefringence and linear dichroism, as observed by differential polarizing optical microscopy. Conductive atomic force microscopy (C-AFM) revealed a 42-fold improvement in out-of-plane hole mobility through crystals adopting the vertical molecular orientation compared to those adopting the horizontal molecular orientation.

Flexible organic field-effect transistors with TIPS-Pentacene crystals exhibiting high electrical stability upon bending

Flexible organic field-effect transistors with high electrical stability upon bending are demonstrated on indium tin oxide coated polyethylene terephthalate substrates with TIPS-Pentacene semiconductor crystals formed by drop casting on a hybrid gate dielectric consisting hafnium dioxide grown by atomic layer deposition and spin coated poly(4-vinylphenol). Fabricated devices exhibited excellent p-channel characteristics with field-effect mobility up to 0.12 cm2/Vs with high current on/off ratio >104 and low threshold voltage of −0.2 V. Device performance was slightly affected by mechanical strain applied by bending for 5 min with radius varying from 12.5 mm to as low as 5.0 mm; and a high stability in performance was demonstrated upon applying constant tensile strain for more than 48 h at bending radius of 5.0 mm. It was found that strain induced changes in the device performance primarily occur due to increase in dielectric surface roughness; and the semiconductor-dielectric interface uniformity is influenced more with magnitude of strain rather than its duration.

Homogeneous Crystallization of Micro-DispensedTIPS-Pentacene Using a Two-Solvent System toEnable Printed Inverters on Foil Substrates

We report on a micro-dispensing system for 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) to enable homogenous crystallization and uniform filmmorphology of the dispensed droplets using a two-solvent mixture along with the use of aninsulating binder. This solution composition results in a controlled evaporation of the dropletin ambient air such that the Marangoni flow counteracts the outward convective flow toenable uniform radial crystal growth from the edge towards the center of the drops.The consequence of this process is the high degree of uniformity in the crystallization of thedrops, which results in a reduction in the performance spread of the organic field effecttransistors (OFET) created using this process. The addition of the insulating binder furtherimproves the reduction in the spread of the results as a trade-off to the reduction in mobilityof the transistors. The transfer curves of the OFETs show a tight grouping due to thecontrolled self-alignment of the TIPS-pentacene crystals; this repeatability was furtherhighlighted by fabricating p-type inverters with driver to load ratios of 8:1, wherein theoutput inverter curves were also grouped tightly while exhibiting a gain of greater than 4 inthe switching region. Therefore, the reliability and repeatability of this process justifies itsuse to enable large area solution-processed printed circuits at the cost of reduced mobility.

Fabrication of highly oriented large-scale TIPS pentacene crystals and transistors by the Marangoni effect-controlled growth method.

We demonstrate a solution method of Marangoni effect-controlled oriented growth (MOG) to fabricate highly oriented crystals of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) on the Si/SiO2 substrate. Based on the Marangoni effect induced by mixed solvent systems, large area aligned ribbon crystals can be achieved, covering over 60% on 4 cm × 1 cm Si/SiO2 substrates. We investigated the growth mechanism of the MOG method and found that the correct choice of solvents and appropriate solvent ratios are in favor of aligned crystal growth. With the ribbon crystals of TIPS pentacene, top-contact organic field-effect transistors are fabricated. The optimal device exhibits a field-effect mobility of 0.70 ± 0.22 cm(2) V(-1) s(-1) and an on/off ratio of 10(5). The MOG method, which has potential to be used in batch production and features easy control of crystal growth using non-contact forces, will benefit the development of low-cost, high-performance, organic semiconductor devices.

Laterally-stacked, solution-processed organic microcrystal with ambipolar charge transport behavior.

We report the formation of laterally stacked ambipolar crystal wire for high-mobility organic field-effect transistors (OFETs), along with a simple logic circuit through a solution process. A soluble pentacene derivative, 6,13-bis(triisopropylsilylethynyl)pentacene (Tips-pentacene), and N,N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) were used as p-type and n-type organic semiconductors, respectively. The laterally stacked ambipolar crystal wire is made up of Tips-pentacene and PTCDI-C8 crystals in a structure of Tips-pentacene/PTCDI-C8/Tips-pentacene (TPT). The inner part of the crystal is made up of PTCDI-C8, and Tips-pentacene is present on both sides. These TPT crystals exhibit typical ambipolar charge transport behavior in organic electronic devices, which show very balanced hole and electron mobility as high as 0.23 cm(2)/V·s and 0.13 cm(2)/V·s, respectively. Static and dynamic operational stability of the device is investigated by measuring the device performance as a function of storage time and applying voltage pulse, respectively, and it shows good air stability. In addition, a simple logic circuit based on the TPT crystal wire has been fabricated, and the static and dynamic performance has been evaluated. The results indicate that the TPT crystals are potentially useful for miniaturized organic electronic devices.

Temperature gradient approach to grow large, preferentially oriented 6,13-bis(triisopropylsilylethynyl) pentacene crystals for organic thin film transistors

In this study, 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene crystalline growth was enhanced using temperature gradient across the substrate. This method induced a preferential crystal orientation in order to alleviate the intrinsic crystallization anisotropy and control film morphology. The temperature gradient led to a solubility difference along the substrate and drove crystallization from the lower-temperature end to the higher. The approach also enables a methodical investigation of how TIPS pentacene crystal morphology depends on temperature. The resulting TIPS pentacene film exhibited a uniform morphology and high percentage of large areal coverage. X-ray diffraction characterization showed that the film crystallinity was not sacrificed when a temperature gradient is applied. The authors demonstrated that organic thin film transistors (OTFTs) based on TIPS pentacene crystals grown using the temperature-gradient method significantly enhanced average mobility when compared to OTFTs using films grown without the temperature gradient.

High‐Mobility, Aligned Crystalline Domains of TIPS‐Pentacene with Metastable Polymorphs Through Lateral Confinement of Crystal Growth

Patterns composed of solvent wetting and dewetting regions promote lateral confinement of solution-sheared and lattice-strained TIPS-pentacene crystals. This lateral confinement causes aligned crystal growth, and the smallest patterns of 0.5 μm widesolvent wetting regions promotes formation of highly strained, aligned, and single-crystalline TIPS-pentacene regions with mobility as high as 2.7 cm(2) V(-1) s(-1) .

Inkjet-printed organic thin film transistors based on TIPS pentacene with insulating polymers

The blending of the crystalline organic semiconductor, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene), with amorphous polymers exhibits not only excellent solution processability, but also superior performance characteristics in organic thin film transistors (OTFTs). To understand the inkjet-printing behavior of TIPS pentacene/polymer blends, we use amorphous polycarbonate (APC), which is structurally beneficial to the facile phase separation of TIPS pentacene crystals due to the strong segregation strength estimated by the Flory–Huggins interaction parameter. The various inkjet-printing behaviors of TIPS pentacene/APC inks, which depend on the TIPS pentacene/APC compositions, ink viscosities, and different solvent mixtures, are investigated. These behaviors can ultimately determine the phase separation, morphology, shape, and orientation of the TIPS pentacene crystals in OTFT films. Flory–Huggins phase separation theory is applied, and various analytical methods, such as polarized optical microscopy, 3D surface profile, and time-of-flight secondary ion mass spectroscopy (TOF-SIMS), are utilized to explain these relationships. By controlling these inkjet-printing conditions, it is possible to easily regulate the optimal inkjet-printing process for TIPS-pentacene/polymer systems, which can derive the desirable stripe-shaped and vertically phase-separated TIPS pentacene crystals with the proper orientation and enhanced surface morphology. The resultant inkjet-printed films from the TIPS pentacene with APC show excellent device stability and an average mobility of 0.53 cm2 V−1 s−1. Furthermore, the inkjet-printed flexible OTFT array with an average mobility of 0.27 cm2 V−1 s−1 sustains the application of TIPS pentacene/APC in the field of flexible printed electronics.

Uniaxial alignment of triisopropylsilylethynyl pentacene via zone-casting technique

Uniaxially aligned triisopropylsilylethynyl pentacene (TIPS-pentacene) crystals over a large area were fabricated using zone-casting technique. The array of TIPS-pentacene displayed a high orientation degree with a dichroic ratio (DR) of 0.80. The crystals were arranged with c axis perpendicular to the substrate and the long axis of the ribbon corresponded to the a axis of TIPS-pentacene. The properties of the solutions and the processing parameters were shown to influence the formation of the oriented TIPS-pentacene crystalline array. Solvent with a low boiling point (such as chloroform) favoured the orientation of the ribbon-like crystals. The concentration of the solution should be appropriate, ensuring the crystallization velocity of TIPS-pentacene matching with the receding of the meniscus. Besides, we proved that the casting speed should be large enough to induce a sufficient concentration gradient. The orientation mechanism of TIPS-pentacene was attributed to a synergy of the ordered nuclei and a match between the crystallization velocity and the casting speed. Field effect transistors (FETs) based on the oriented TIPS-pentacene crystalline array showed a mobility of 0.67 cm(2) V(-1) s(-1).

去润湿图案化制备TIPS-并五苯有机薄膜晶体管

Top-contact organic thin-film transistors array was prepared by slectively dewetting of 6,13-Bis(triisopropylsilylethynyl) pentacene(TIPS-Pentacene) solution.The optical microscope images showed that the morphology of TIPS-pentacene crystal was influenced by the rotation speed.The TIPS-pentacene thin-films prepared at 1 000~2 000 r/min had good connectivity and large crystal domains.As the rotation speed increased to 3 000 r/min,the patterned film became incomplete and the crystal domain size reduced.The output and transfer curve,on/off current ratio,threshold voltage and field-effect mobility of the device were obtained by electric measurements.The TIPS-pentacene OTFTs prepared at 1 000 r/min had a maximum field-effect mobility of up to 5.16×10-2 cm·V-1·s-1 and an on/off current ratio of 8×103.

Air-flow navigated crystal growth for TIPS pentacene-based organic thin-film transistors

6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) is a promising active channel material of organic thin-film transistors (OTFTs) due to its solubility, stability, and high mobility. However, the growth of TIPS pentacene crystals is intrinsically anisotropic and thus leads to significant variation in the performance of OTFTs. In this paper, air flow is utilized to effectively improve the TIPS pentacene crystal orientation and enhance performance consistency in OTFTs, and the resulted films are examined with optical microscopy, X-ray diffraction, and thin-film transistor measurements. Under air-flow navigation (AFN), TIPS pentacene drop-cast from toluene solution has been observed to form thin films with improved crystal orientation and increased areal coverage on substrates, which subsequently lead to a fourfold increase of average hole mobility and one order of magnitude enhancement in performance consistency defined by the ratio of average mobility to the standard deviation of the field-effect mobilities.

High-performance organic thin film transistors based on inkjet-printed polymer/TIPS pentacene blends

The blending of crystalline organic semiconductor, 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS pentacene) with amorphous polymers exhibits not only excellent solution processibility but also superior performance characteristics in organic thin film transistors (OTFTs). To understand the inkjet printing behavior of polymer/TIPS pentacene blends, we synthesized triarylamine-based polymers with various polarities, which were obtained by changing the fluorine content in the polymer structure. The variation of segregation strength of the polymer domains in the blends can be induced depending on the different polarities of the polymers, which can ultimately determine the shape and orientation of the TIPS pentacene crystals in OTFT films. This relationship was explained by the Flory–Huggins phase separation theory according to the measured TFT performance. Polarized optical microscopy, 3D surface profile, and X-ray diffraction (XRD) were used to investigate the crystal orientation, surface morphology, and crystallinity of the polymer/TIPS pentacene thin films. The experimental results suggest that the phase separation behavior between the polymer and TIPS pentacene plays a significant role in the formation of crystal structure of TIPS pentacene in the film. The moderate segregation of the polymers from the TIPS pentacene crystal domains effectively derives the desirable stripe-shaped crystals with the proper orientation and enhanced surface morphology. The resultant inkjet-printed films from the triarlyamine-based polymers with TIPS pentacene showed excellent mobility of 0.14–0.19cm2V−1s−1, which are among the highest values obtained by inkjet printing reported to date.

Use of a hexapod in diffraction measurements of substrate-supported crystals of organic semiconductors

Thin films of organic semiconductor prepared on substrates generally contain crystals that have one common crystal plane parallel to the substrate but random in-plane orientations. In diffraction measurements of these structures, it is often required to anchor the X-ray beam on a fixed spot on the sample, such as an optically visible crystallite or island. Here, a hexapod is used in place of a traditional multi-circle diffractometer to perform area-detector-based diffraction measurements on an actual device that contains 6,13-bis(triisopropyl-silyethynyl)-pentacene (TIPS-pentacene) crystals. The hexapod allows for sample rotations about any user-defined rotation center. Two types of complex sample motions have been programmed to characterize the structure of the TIPS-pentacene crystal: an in-plane powder average has been performed at a fixed grazing-incident angle to determine the lattice parameters of the crystal; then the in-plane component of the scattering vector was continuously rotated in transmission geometry to determine the local crystal orientation.