TIPS Pentacene Research Articles

Influence of phase-separated morphology on small molecule/polymer blend organic field-effect transistors fabricated using electrostatic spray deposition

Bottom-gate top-contact organic field-effect transistors (OFETs) based on 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) and poly(methyl methacrylate) (PMMA) blends were fabricated using electrostatic spray deposition (ESD). Solvent-vapor annealing (SVA) was conducted as a post-deposition treatment to induce vertical phase separation of the blend films. The phase-separated morphology was investigated by selective etching of TIPS pentacene with cyclohexane. A relatively rough surface with some pinholes was observed in the etched film without SVA, suggesting that vertical phase separation was not sufficient during the ESD process. The phase-separated morphology was modified remarkably by SVA, and a SVA-treated blend device with a well-defined phase-separated structure exhibited enhanced performance and operational stability compared to a device based on the as-deposited blend.

Vertical phase separation of 6,13-bis(triisopropylsilylethynyl) pentacene/poly(methyl methacrylate) blends prepared by electrostatic spray deposition for organic field-effect transistors

Blend films composed of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) and poly(methyl methacrylate) (PMMA) were prepared by electrostatic spray deposition (ESD). ESD is considered as an intermediate process between dry and wet processes since the solvent present in small droplets can almost be evaporated before arriving at the substrate. Post-drying treatments with the time-consuming evaporation of residual solvents can be omitted. However, it is still not clear that a vertically phase-separated structure can be formed in the ESD process since the vertical phase separation of the blend films is associated with the solvent evaporation. In this study, we fabricated bottom-gate, top-contact organic field-effect transistors based on the blend films prepared by ESD and the devices exhibited transistor behavior with small hysteresis. This result demonstrates that the vertical phase separation of a blend film (upper TIPS pentacene active layer/bottom PMMA gate insulator) can occur in the facile one-step ESD process.

TIPS pentacene loaded PEO-PDLLA core-shell nanoparticles have similar cellular uptake dynamics in M1 and M2 macrophages and in corresponding in vivo microenvironments

Nanoparticle based drug delivery platforms have the potential to transform disease treatment paradigms and therapeutic strategies, especially in the context of pulmonary medicine. Once administered, nanoparticles disperse throughout the lung and many are phagocytosed by macrophages. However, there is a paucity of knowledge regarding cellular up-take dynamics of nanoparticles due largely to macrophage heterogeneity. To address this issue, we sought to better define nanoparticle up-take using polarized M1 and M2 macrophages and novel TIPS-pentacene loaded PEO-PDLLA nanoparticles. Our data reveal that primary macrophages polarized to either M1 or M2 phenotypes have similar levels of nanoparticle phagocytosis. Similarly, M1 and M2 polarized macrophages isolated from the lungs of mice following either acute (Th1) or allergic (Th2) airway inflammation also demonstrated equivalent levels of nanoparticle up-take. Together, these studies provide critical benchmark information pertaining to cellular up-take dynamics and biodistribution of nanoparticles in the context of clinically relevant inflammatory microenvironments.

Sub-10 fs Time-Resolved Vibronic Optical Microscopy.

We introduce femtosecond wide-field transient absorption microscopy combining sub-10 fs pump and probe pulses covering the complete visible (500–650 nm) and near-infrared (650–950 nm) spectrum with diffraction-limited optical resolution. We demonstrate the capabilities of our system by reporting the spatially- and spectrally-resolved transient electronic response of MAPbI3–xClx perovskite films and reveal significant quenching of the transient bleach signal at grain boundaries. The unprecedented temporal resolution enables us to directly observe the formation of band-gap renormalization, completed in 25 fs after photoexcitation. In addition, we acquire hyperspectral Raman maps of TIPS pentacene films with sub-400 nm spatial and sub-15 cm–1 spectral resolution covering the 100–2000 cm–1 window. Our approach opens up the possibility of studying ultrafast dynamics on nanometer length and femtosecond time scales in a variety of two-dimensional and nanoscopic systems.

Current‐Induced Joule Heating and Electrical Field Effects in Low Temperature Measurements on TIPS Pentacene Thin Film Transistors

The channel temperature (Tch) of solution‐processed 6,13‐bis(triisopropylsilylethynyl)‐pentacene (TIPS pentacene) thin film transistors (TFTs) is closely monitored in real time during current–voltage (I–V) measurements carried out in a He exchange gas cryostat at various base temperatures (Tb) between 300 K and 20 K. This is done using a platinum (Pt) resistance temperature sensor embedded within the transistor channel. Under large gate (Vg) and source‐drain (Vds) voltage biases, an increase inTchis observed, the magnitude of which depends on the thermal conductivity of the substrate. The increase inTchis associated with a simultaneous increase in the transistor drain current (Id) and becomes particularly pronounced at cryogenicTb. These experimental observations are rationalized using a 1D theoretical model and are attributed to current‐induced Joule heating. However, even though the heating of the channel unquestionably plays an important role, the corresponding amount of increase inIdat cryogenicTband large voltage biases cannot be fully accounted for unless at low temperatures μTIPSis enhanced in the presence of strong electrical fields. Therefore it is concluded that theI–Vcharacteristics of TIPS pentacene TFTs at lowTband large voltage biases are a result of a complex interplay between current‐induced Joule heating and electrical field effects.

Characteristics of terahertz wave modulation using wavelength-selective photoexcitation in pentacene/Si and TIPS pentacene/Si bilayers

We demonstrate the characteristics of the optical control of terahertz (THz) wave transmission in photoexcited bilayers of pentacene/Si and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene)/Si. The modulation efficiency is influenced significantly by the photoexcitation wavelength of the optical beams. Lower optical absorption of organic materials leads to higher modulation efficiency because the photocarriers excited on Si with a higher diffusion rate and mobility are far more instrumental in increasing the modulation than the excitons generated on the organic layers. Securing a sufficient depth for carrier diffusion on organic layers is also important for increasing the THz modulation efficiency. These findings may be useful for designing highly efficient and spectrally controllable THz wave modulators.

Temperature gradient controlled crystal growth from TIPS pentacene-poly(α-methyl styrene) blends for improving performance of organic thin film transistors

6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) from simple drop casting typically forms crystals with random orientation and poor areal coverage, which leads to device-to-device performance variation of organic thin film transistors (OTFTs). Previously, a temperature gradient technique was developed to address these problems. However, this approach simultaneously introduced thermal cracks due to the thermally induced stress during crystallization. These thermal cracks accounted for a reduction of charge transport, thereby impacting the device performance of TIPS pentacene based OTFTs. In this work, an insulating polymer, poly(α-methyl styrene) (PαMS) was blended with TIPS pentacene to relieve the thermal stress and effectively prevent the generation of thermal cracks. The results demonstrate that the incorporation of PαMS polymer combined with the temperature gradient technique improves both the hole mobility and performance consistency of TIPS pentacene based OTFTs.

Influence of substrate temperature and overlap condition on the evaporation behavior of inkjet-printed semiconductor layers in organic thin film transistors

In this study, we investigate the evaporation behavior of inkjet-printed semiconductor layers of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) to obtain well-oriented crystalline structures for the fabrication of high-performance organic thin film transistors (OTFTs). Variations in overlap and substrate temperature are considered to control the evaporation behavior and the resulting crystalline structures of the layers. The internal flow and corresponding contact line movement can be controlled via three representative inkjet-printing regimes. For inkjet-printing regimes that induce outward convective flow (the coffee stain effect), randomly-oriented TIPS pentacene crystalline structures are produced by irregular contact line receding. With an optimized inkjet-printing regime, uniform bottom contact line movement is generated by the unidirectional internal flow, resulting in well-oriented crystalline structures. All-inkjet-printed OTFTs with semiconductor layers inkjet-printed using the optimized regime exhibit a high field effect mobility of ~0.13cm2/Vs, due to the one-dimensionally-oriented TIPS pentacene crystal arrays.

Terahertz modulation using TIPS-pentacene thin films deposited on patterned silicon substrates

We demonstrate the characteristics of terahertz (THz) wave modulation by 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) thin films deposited on silicon substrates patterned with one-dimensional periodic multi-channels. The polarization independence of the THz wave modulation in the hybrid structures with one-dimensional channels indicates that the rapid in-plane diffusion of the carriers injected into the TIPS pentacene thin films plays an important role in the high modulation of THz waves. Understanding the mechanisms of THz modulation is important for optimizing the performance of THz devices based on organic/inorganic hybrid structures.

Aligned growth of TIPS pentacene crystalline domains adhered to Au stripes formed on SiO2 surfaces

6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was electrosprayed onto SiO2/Si substrates with Au stripes, and we observed that the crystalline domains adhered to the Au stripes were preferentially oriented. To understand this phenomenon, the dynamic behavior of a microdroplet on the Au-striped SiO2 surface was studied based on real-time monitoring. We found that the contact line of the microdroplet proceeded along the Au stripe. Since crystallization occurs at the contact line, TIPS pentacene can grow as the contact line proceeds along the Au stripe. Therefore, the fast growth axis in the TIPS pentacene crystal structure can be aligned in the stripe direction. This consideration was supported by the result of angle-dependent polarized Raman spectroscopy of the crystalline domains adhered to the Au stripes.

Optimization and improvement of TIPS–pentacene transistors (OTFT) with UV–ozone and chemical treatments using an all-step solution process

We fabricated an organic thin-film transistor (OTFT) using an all-step solution process. The printed layers, in which the electrode (silver), dielectric layer (BaTiO3–PMMA), source–drain layer, and semiconductor 6,13-Bis(triisopropylsilylethynyl)pentacene(TIPS–pentacene), were optimized using roll-to-roll, an inkjet printer, and drop-casting. After coating the source–drain layer, we applied ultraviolet (UV)–ozone and self-assembled monolayer (SAM) treatments to the composite layer. The OTFTs treated with the UV–ozone and SAM treatments were found to exhibit excellent performance and good properties in comparison to silicon-based OTFTs.

Organic field-effect transistors based on single-crystalline active layer and top-gate insulator consistently fabricated by electrostatic spray deposition

An electrostatic spray deposition (ESD) method was applied to prepare both crystalline domains of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) and insulating films of poly(methyl methacrylate) (PMMA) for fabricating top-gate single-crystal organic field-effect transistors (OFETs). The electrical characteristics of the top-gate device were compared to those of the bottom-gate one (SiO2 bottom-gate insulator) with the same active layer, and the lower charge-trap density at the interface between the top-gate insulator and single-crystalline active layer was demonstrated. The drain current compression in the output characteristics of the top-gate device, however, occurred due to the large parasitic resistance between the source/drain electrodes and accumulation channel. Reducing the thickness of the single-crystalline active layer resulted in a high charge-carrier mobility of 0.29cm2/Vs (channel length of 5μm).

Control of the crystalline structure of inkjet-printed semiconductor layers using overlap condition and surface wettability

We demonstrate the effects of overlap condition and surface wettability of dielectric layers on the drying process and crystalline structure of inkjet-printed semiconductor layers. 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was utilized to inkjet-print the semiconductor layer. Using various overlap conditions, semiconductor layers were inkjet-printed on dielectric layers with different surface wettabilities. It is observed that crystal growth and the resulting crystalline structures in inkjet-printed semiconductor layers are primarily determined by evaporation behavior, particularly the contact line movement of the drying semiconductor layers, which can be controlled via the overlap condition. With inappropriate overlap conditions, randomly oriented TIPS pentacene crystalline structures are generated in the semiconductor layer through irregular contact line recession. One-dimensionally oriented TIPS pentacene crystal structures can be obtained using the optimized overlap condition of 50% as a result of the uniform contact line movement. Relatively hydrophobic dielectric layers help to generate good crystallinity in the semiconductor layer. All-inkjet-printed organic thin film transistors (OTFTs) with well-oriented TIPS pentacene crystalline structures in the semiconductor layer show a high field effect mobility of ~0.1 cm2 V−1s−1, suggesting that, when printing inkjet semiconductor layers, the overlap condition and surface wettability of the dielectric layer are important factors for generating a well-oriented crystalline structure and thereby fabricating high-performance all-inkjet-printed OTFTs.

Band-like transport observed in TIPS-pentacene thin film by time-resolved microscopic optical second-harmonic generation imaging

Carrier transport in single-crystalline grains of 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene was studied using time-resolved microscopic optical second-harmonic generation (TRM-SHG). TRM-SHG is used to directly visualize carrier injection and transport behavior in TIPS pentacene. A strong SHG signal observed at the edge of a FET source electrode at low temperature suggests the presence of a potential drop associated with the carrier injection process. An accurate carrier mobility calculation, taking into account the potential drop, shows a negative slope with temperature that indicates band-like transport.

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.

Angle-Dependent Polarized Raman Spectroscopy of TIPS Pentacene Single-Crystalline Domains Deposited on Au-Striped Substrates

ABSTRACT6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was deposited on SiO2/Si substrates with Au stripes using electrostatic spray deposition (ESD). We observed that crystalline domains on the substrates were preferentially oriented. To elucidate this phenomenon, the correlation between the orientation direction and stripe direction was investigated by angle-dependent polarized Raman spectroscopy. Since the acene planes in TIPS pentacene take an edge-on orientation on the substrates, C-C ring stretch modes can be used to probe the in-plane orientation. We found that the long molecular axis of acene planes is inclined at about 50° or 110° from the stripe direction. This result suggests that the molecular orientation of the crystalline domains can be controlled by the stripes.

Volatilize-Controlled Oriented Growth of the Single-Crystal Layer for Organic Field-Effect Transistors

We demonstrate a solution method of volatilize-controlled oriented growth (VOG) to fabricate aligned single crystals of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) on a Si/SiO2 substrate. Through controlling the evaporation rate of the solvent, large-area-aligned single-crystal layers can be achieved on several substrates at the same time, covering over 90% on 2 × 1 cm substrates. The method provides a low-cost, maneuverable technology, which has potential to be used in batch production. We find that the atmosphere of the solvent with high dissolving capacity is in favor of aligned single-crystal growth. Besides, the growth mechanism of the VOG method is investigated in this paper. Top-contact organic field-effect transistors based on the single crystals of TIPS pentacene are achieved on a Si/SiO2 substrate. The optimal device exhibits a field-effect mobility of 0.42 cm(2) V(-1) s(-1) and an on/off current ratio of 10(5). Our research indicates that the VOG method is promising in single-crystal growth on a Si/SiO2 substrate for commercial production.

Impact of Intermolecular Distance on Singlet Fission in a Series of TIPS Pentacene Compounds.

Singlet fission has attracted considerable interest for its potential application in organic photovoltaics. However, the underlying microscopic mechanism is not well understood and the molecular parameters that govern SF efficiency remain unclear. We herein study the primary exciton photogeneration and evolution in the thin film of a series of pentacene derivatives (TIPS-Pn and ADPD-Pn) using femtosecond transient absorption spectroscopy. With a favorable "long-edge on" packing motif, the singlet-excited slip-stacked TIPS-Pn and ADPD-Pn molecules undergo ultrafast fission to produce triplet excitonic states with time constants of ∼0.3 ps. More importantly, the ADPD-Pn compound features a considerably higher triplet yield than TIPS-Pn (162 ± 10% vs 114 ± 15%). The enhanced electronic coupling as a result of closer interchromophore distance (3.33 Å for ADPD-Pn vs 3.40 Å for TIPS-Pn) is suggested to account for the much higher triplet yield for ADPD-Pn relative to that for TIPS-Pn, proving SF can be readily modulated by adjusting the intermolecular distance.

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.

Blending effect of 6,13-bis(triisopropylsilylethynyl) pentacene–graphene composite layers for flexible thin film transistors with a polymer gate dielectric

Solution processible poly(4-vinylphenol) is employed as a transistor dielectric material for low cost processing on flexible substrates at low temperatures. A 6,13-bis (triisopropylsilylethynyl) (TIPS) pentacene–graphene hybrid semiconductor is drop cast to fabricate bottom-gate and bottom-contact field-effect transistor devices on flexible and glass substrates under an ambient air environment. A few layers of graphene flakes increase the area in the conduction channel, and form bridge connections between the crystalline regions of the semiconductor layer which can change the surface morphology of TIPS pentacene films. The TIPS pentacene–graphene hybrid semiconductor-based organic thin film transistors (OTFTs) cross-linked with a poly(4-vinylphenol) gate dielectric exhibit an effective field-effect mobility of 0.076 cm2 V−1 s−1 and a threshold voltage of −0.7 V at V gs = −40 V. By contrast, typical TIPS pentacene shows four times lower mobility of 0.019 cm2 V−1 s−1 and a threshold voltage of 5 V. The graphene/TIPS pentacene hybrids presented in this paper can enhance the electrical characteristics of OTFTs due to their high crystallinity, uniform large-grain distribution, and effective reduction of crystal misorientation of the organic semiconductor layer, as confirmed by x-ray diffraction spectroscopy, atomic force microscopy, and optical microscopy studies.