Triisopropylsilyl Ethynyl Research Articles

Wettability‐Assisted Process to Shape Organic Crystalline Printed Films

AbstractThe controlled growth of organic crystalline materials in predefined locations still poses a challenge for functional device application such as phototransistors, photoconductors, or photovoltaic solar cells. This work evidences the use of optical lithography and a fluoroalkylsilane to selectively modify the surface energy and how to create a wettability micro‐patterned structure. These are then combined with non‐contact printing of the organic solution providing custom‐shaped films. To deliver printed films with improved morphological quality, key process parameters for high‐performance organic materials are optimized. Particular attention is given to the adjustment of the concentration and solvent mixture to tune the jetting properties, and consequently, slow down the evaporation rate. Continuous films are obtained for an optimized number of droplets and spacing between them. Micro‐Raman spectroscopy imaging confirms the crystalline nature of the printed films and the lack of impurities. To validate the method, rubrene and triisopropylsilylethynyl (TIPS)‐pentacene are tested using two‐terminal optoelectronic devices. TIPS‐pentacene rectangular printed micrometric photosensor presents linear behavior and no hysteresis, reaching 0.33 nA under 18.1 mW cm−2. The structural and optoelectronic characterization is in line with other micro‐patterned examples, opening doors for new industrial applications.

Structural and Optical Properties of TIPS Pentacene Thin Film Exposed to Gamma Radiation

This study investigates the effects of Gamma-irradiation on the structural, morphological and optical properties of 3,16-bis(tri isopropyl silylethynyl)pentacene (TIPS Pentacene) organic semiconductor films. The TIPS Pentacene thin films were irradiated at 10 to 300 kGy at a dose rate of 1.58 kGy/hr. The films were characterized using X-Ray Diffractometer (XRD), Atomic Force Microscopy (AFM) and Ultraviolet-Visible Spectroscopy (UV-Vis). The XRD analysis showed that the pre-irradiated thin films were of crystalline structure, indicating a broad wave diagram. The XRD and AFM results show that these variations can be attributed to the radiation-induced local heating and microscopic atomic mobility. Based on the UV-Vis results, the thin films exhibit approximately 70% optical transmittance in the visible region at pre-irradiation. At post-irradiation, optical transmittance decreased to 55% at the maximum absorbed dose. The corresponding optical bandgap decreased from 1.87 to 1.50 eV after a total ionizing dose of 300 kGy. The findings showed that TIPS Pentacene thin film has good mitigation towards gamma irradiation and can withstand harsh radiation while retaining its semiconductor properties. It is a potential candidate for flexible electronics for space applications.

Performance Investigation of Organic Thin Film Transistor on Varying Thickness of Semiconductor Material: An Experimentally Verified Simulation Study

Physics-based two-dimensional numerical simulations are performed to analyze the device characteristics of tri-isopropylsilylethynyl (TIPS)-pentacene organic thin-film transistor (OTFT) fabricated using drop-casting technique. Further, using simulation technique enabling calibration this paper also presents the systematic study of the impact of active layer (TIPS-pentacene) thickness on device characteristics. The extracted parameters such as electric field intensity, current density, current On/Off ratio, and mobility exhibit variation with scaling down in active layer thickness from 500 to 100 nm. The study also revealed that Off current and On/Off current ratio (IOn/IOff) is highly dependent on the thickness of the semiconductor layer. Furthermore, the highest value of IOn/IOff is obtained at 100-nm thickness of TIPS-pentacene, which can be used for various fast-switching applications in digital circuits. Simulated results are not only reasonably matching with experimental results but also provide insight on charge transportation at the semiconductor-dielectric interface and in the bulk of TIPS-pentacene layer.

Direct-patterned copper/poly(ethylene oxide) composite electrodes for organic thin-film transistors through cone-jet mode by electrohydrodynamic jet printing

Direct-patterned Cu-based conductive electrodes were printed through electrohydodynamic (EHD) jet printing via cone-jet mode. The introduction of a capping agent in the synthesis of the Cu ink limited excessive conductivity, which enabled the pristine Cu ink to achieve the various printing modes of EHD jet printing: dripping, micro-dripping, cone-jet, and multi-jet. We also obtained optimal printing conditions by adjusting the viscosity by adding poly(ethylene oxide) (PEO) to the pristine Cu inks, resulting in well-defined printing patterns. The optimized PEO content in the ink was determined to be ∼10 wt%, which gave us a stable cone-jet mode and well-defined Cu/PEO composite electrode lines with sharp edges. We utilized the Cu/PEO composite electrode lines as source and drain and a triisopropylsilylethynyl (TIPS)–pentacene/PS blend as the active layer for bottom-gate bottom-contact organic field-effect transistors (OFETs). The resulting devices exhibited an average field-effect mobility (μFET), threshold voltage (Vth), and on/off current ratio (Ion/Ioff) of 0.253 cm2/V, 0.253 V, and ∼106, respectively.

Analysing the TIPSP‐based VOFET through transistor efficiency ( g m /I D )

A simple vertical organic field-effect transistor (VOFET) structure has been fabricated using ambipolar 6, 13-bis (triisopropylsilyl ethynyl) pentacene (TIPSP) with a channel length (L) of 90 nm. This device can operate at –2 V which is much lower than the voltage, reported so far for the organic devices based on TIPSP. The first time, the authors are using transistor efficiency to extract VOFET's parameters. The threshold voltage (V th) of the device has been found to vary between 0.18 and 0.38 V with the current on/off ratio (I on /I off) of 104. The mobility (µ) of the device has been calculated as 0.62 cm2/Vs. The sub-threshold slope, transconductance (gm ), output conductance (g d), and early voltage (V E) have been found to be 140 ± 30 mV/decade, 2 µS, 10−6 S, and 1.3 ± 2 V, respectively.

Tailoring the Emission of Fluorinated Bipyridine-Chelated Iridium Complexes.

New functionalized tris(2′,6′-difluoro-2,3′-bipyridinato-N,C4′)iridium(III) ((dfpypy)3Irs) complexes, including small molecules and their dendrimer embedded analogoues, were synthesized and characterized. It is demonstrated that both the fac-(dfpypy)3Ir-based polyphenylene dendrimers and (triisopropylsilyl)ethynyl (TIPSE)-substituted (dfpypy)3Ir complexes induce large bathochromic shifts (∼50 nm) of emission bands compared with fac-(dfpypy)3Ir. This is due to the pronounced 3π–π* character of emissive excited states and the extended conjugation. A further remarkable feature is the small bathochromic shift of the emissions of fac-tris(2-phenylpyridine)iridium (fac-(ppy)3Ir)-based polyphenylene dendrimers when compared to those of the iridium (Ir) complex core. Obviously, the triplet metal-to-ligand charge transfer makes emission less sensitive to extended conjugation than the 3π–π* transition. This finding suggests new concepts for designing blue phosphorescent dendrimer emitters. Both the dendrimers and the TIPSE-substituted (dfpypy)3Ir complexes represent new green and the trimethylsilyl-functionalized (dfpypy)3Ir new blue phosphorescent emitters. Incorporation of TIPSE moieties into the ligands of iridium complex gives rise to enhanced phosphorescence.

Theoretical design of azaacene-based non-fullerene electron transport material used in inverted perovskite solar cells

ABSTRACTInverted perovskite solar cells (PSCs) have attracted much attention due to their low-temperature and solution-based process. Electron transport layers are important components in inverted PSCs. Non-fullerene n-type organic small molecules seem to be more attractive as electron transport layers, because their structures are easy to be synthesised and modified. In this paper, density functional theory and semi-classical Marcus electron transfer theory were used to explore the electron transport properties in three azaacene derivatives, including one experimentally reported molecule, 1,4,9,16-tetrakis((triisopropylsilyl)ethynyl)quinoxalino[2‴,3‴:4″,5″]cyclopenta[1″,2″,3″:5′,6′]acenaphtho[1′,2′:5,6]pyrazino[2,3-b]phenazine (1), and two theoretically designed molecules (2 and 3). Compound 2 is formed by substituting i-Pr groups in compound 1 with H atoms, which is designed to evaluate the effect of i-Pr groups on the electron transport properties. Compound 3 is designed by adding one more benzopyrazine group to the conjugation structure of compound 1. It shows that i-Pr group can increase HOMO and LUMO energy levels and improve solubility in organic solvent and hydrophobicity. Enlarging conjugation can not only decrease LUMO energy level and electron reorganisation energy, but also can increase solubility and electron mobility. So our designed compound 3 is expected to be a potential electron transport material in inverted PSCs.

Incorporating Trialkylsilylethynyl-Substituted Head-to-Head Bithiophene Unit into Copolymers for Efficient Non-Fullerene Organic Solar Cells.

Mediating the backbone coplanarity and solubility of oligothiophenes, especially the head-to-head (HH) disubstituted bithiophene, to achieve an optically and electronically advantageous building block for organic semiconductor materials is a vital yet challenging task. On the other hand, exploring polymer solar cells (PSCs) processed from nonhalogenated solvents is necessary toward their large-scale applications. In this contribution, we develop a HH-type bithiophene analogue (TIPS-T2) by strategically applying the triisopropylsilylethynyl (TIPS) scaffold as the side chain. TIPS can serve to narrow optical band gaps, lower the highest occupied molecular orbital level, reduce intrachain steric hindrance, and guarantee sufficient solubility of the involving polymers. Upon alternating with difluorobenzotriazole (FTAZ) or benzodithiophene-4,8-dione (BDD) acceptor units, two polymers named PT4Si-FTAZ and PT4Si-BDD are synthesized. Encouragingly, non-fullerene PSCs incorporating PT4Si-FTAZ yield a power conversion efficiency of 6.79% when processed from an environment-friendly solvent of trimethylbenzene because of its promoted backbone planarity, as demonstrated by density functional theory, higher hole mobility, and superior film morphology. The results indicate that TIPS-T2 is a promising building block for constructing photovoltaic polymers, and our findings offer an avenue for the ingenious use of TIPS as functional side chains.

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.

Optical, Electrochemical and Thermal Studies of Conjugated Polymers Synthesized by Eutectic Melt Reaction.

This paper reports on the synthesis of a novel donor-acceptor conjugated polymers, P1 and P2 by solvent free eutectic melt polymerization reaction. Triisopropylsilylethynyl(TIPS) substituted benzo[1,2-b:4,5-b']dithiophene(BDT) is used as donor, thienithiophene(TT) and thienopyrroledione(TPD) are utilized as acceptors for demonstrating eutectic polymerization. The most important fact in the solvent-free reaction between solid reactants actually proceeds through bulk liquid phases. Such liquid phases are possible due to the formation of eutectics between the reactants and product(s) and any evolution of heat. Naphthalene is explored in this reaction for forming eutectics with the reactants, resulting in desired polymers. Thermal stability, optical and electrochemical properties of these polymers were determined. Optical band gaps of the polymers were found to be 1.58 and 1.65eV. Electrochemical studies by cyclic voltametry experiment revealed HOMO and LUMO energy levels to be -5.22, -5.60eV, and -3.76, -4.16eV, respectively. The polymers were thermally stable up to 285-400°C. Thermal, optical and electrochemical studies indicated these materials to be promising candidates in organic electronic applications.

Influence of orientation mismatch on charge transport across grain boundaries in tri-isopropylsilylethynyl (TIPS) pentacene thin films.

We present a multi-scale model for charge transport across grain boundaries in molecular electronic materials that incorporates packing disorder, electrostatic and polarisation effects. We choose quasi two-dimensional films of tri-isopropylsilylethynyl pentacene (TIPS-P) as a model system representative of technologically relevant crystalline organic semiconductors. We use atomistic molecular dynamics, with a force-field specific for TIPS-P, to generate and equilibrate polycrystalline two-dimensional thin films. The energy landscape is obtained by calculating contributions from electrostatic interactions and polarization. The variation in these contributions leads to energetic barriers between grains. Subsequently, charge transport is simulated using a kinetic Monte-Carlo algorithm. Two-grain systems with varied mutual orientation are studied. We find relatively little effect of long grain boundaries due to the presence of low impedance pathways. However, effects could be more pronounced for systems with limited inter-grain contact areas. Furthermore, we present a lattice model to generalize the model for small molecular systems. In the general case, depending on molecular architecture and packing, grain boundaries can result in interfacial energy barriers, traps or a combination of both with qualitatively different effects on charge transport.

Theory-Driven Insight into the Crystal Packing of Trialkylsilylethynyl Pentacenes

The functionalization of oligoacenes and similar π-conjugated chromophores with trialkylsilylethynyl groups has proven to be a versatile means to enhance solubility and solution processability and engineer solid-state packing arrangements to produce organic semiconductors that demonstrate outstanding charge-carrier transport characteristics. While a general, empirical-based geometric model has been developed and implemented to direct the solid-state packing arrangements of these molecular materials, there exist numerous examples where the model falters. Here, we employ electronic structure methods to probe the noncovalent, intermolecular interactions of two closely related systems that result in two very different crystal packing configurations: triisopropylsilylethynyl (TIPS) pentacene and its triethylsilylethynyl (TES) analog. The quantum-chemical evaluation details how the slightly larger electron density contained within the volume of the TIPS moiety with respect to TES is in part responsible for the ...

Synthesis and Photophysical Studies of Thiadiazole[3,4-c]pyridine Copolymer Based Organic Field-Effect Transistors.

A novel thiadiazolo[3,4-c]pyridine]based donor-acceptor (D-A) copolymer, poly[4,8-bis(triisopropylsilylethynyl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-[4,7-bis(4-(2-ethylhexyl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-c]pyridine] (PTBDTPT), containing triisopropylsilylethynyl(TIPS)benzo[1,2-b:4,5-b']dithiophene as a donor is synthesized by Stille polymerization reaction. All the important photo physical prerequisites for organic field-effect transistor (OFET) application such as strong and broad optical absorption, thermal stability, and compatible HOMO-LUMO levels can be accomplished and combined on one macromolecule. Optical band gap of the polymer was found to be 1.61eV as calculated from its film onset absorption edge. The hole mobility of bottom gate OFET using the synthesized polymer as an active channel is found to be 1.92 X 10(-2)cmV(-1)s(-1) with the On/Off ratio of 25. The photophysical study suggests that PTBDTPT is promising candidate for future large area organic electronic applications.

Unveiling Singlet Fission Mediating States in TIPS-pentacene and its Aza Derivatives.

Femtosecond pump-depletion-probe experiments were carried out in order to shed light on the ultrafast excited-state dynamics of triisopropylsilylethynyl (TIPS)-pentacene and two nitrogen-containing derivatives, namely, diaza-TIPS-pentacene and tetraaza-TIPS-pentacene. Measurements performed in the visible and near-infrared spectral range in combination with rate model simulations reveal that singlet fission proceeds via the extremely short-lived intermediate (1)TT state, which absorbs in the near-infrared spectral region only. The T1 → T3 transition probed in the visible region shows a rise time that comprises two components according to a consecutive reaction (S1 → (1)TT → T1). The incorporation of nitrogen atoms into the acene structure leads to shorter dynamics, but the overall triplet formation follows the same kinetic model. This is of particular importance, since experiments on tetraaza-TIPS-pentacene allow for investigation of the triplet state in the visible range without an overlapping singlet contribution. In addition, the pump-depletion-probe experiments show that the triplet absorption in the visible (T1 → T3) and near-infrared (T1 → T2) regions occurs from the same initial state, which was questioned in previous studies. Furthermore, an additional ultrafast transfer between the excited triplet states (T3 → T2) is identified, which is also in agreement with the rate model simulation. By applying depletion pulses, which are resonant with higher vibrational levels, we gain insight into internal vibrational energy redistribution processes within the triplet manifold. This additional information is of great relevance regarding the study of loss channels within these materials.

Triisopropylsilylethynyl substituted benzodithiophene copolymers: synthesis, properties and photovoltaic characterization

We demonstrated herein the facile synthesis of triisopropylsilylethynyl (TIPS) functionalized benzo[1,2-b:4,5-b′]dithiophene (BDT) for efficient polymer solar cells.

Diporphyrin magnesium complex with long-wavelength light absorption for organic solar cells

We synthesized a diporphyrin compound [4,7-bis[5-[arylethynyl]-10,20-bis{(triisopropylsilyl)ethynyl}porphyrin-15-yl]]-2,1,3-benzothiadiazole dimagnesium(II)], in which two porphyrin units were linked using a benzodiathiazole unit as an electron-withdrawing moiety. These diporphyrins have low-lying HOMO and LUMO levels with long-wavelength light absorption property. Power conversion efficiency of the organic solar cell using this diporphyrin and mix-PCBM (a 85:15 mixture of [6,6]-phenyl- C 61-butyric acid methyl ester ( PC 61 BM ) and [6,6]-phenyl- C 71-butyric acid methyl ester ( PC 71 BM ) was 2.75% with short-circuit current density of 8.79 mA/cm2, open-circuit voltage of 0.80 V, and fill factor of 0.39. Photocurrent conversion in the near infrared region was demonstrated by the incident photon-to-current efficiency spectrum.

Halogen Bonding in Diaza-Triisopropylsilyl-Tetracene Crystals?

Four halogenated triisopropylsilylethynyl (TIPS)-tetracene derivatives were synthesized, their single crystal structures and optical and electronic properties were examined. Both, diiodo-TIPS-diazatetracene and dibromo-TIPS-diazatetracene showed herringbone arrangements, in which the halogen atoms are directed toward the nitrogen atoms of a neighboring molecule with slightly lower distances than the van der Waals radii between halogen and nitrogen atoms. Computations of the electrostatic potentials showed the availability and the strength of σ holes, so that we assume a weak halogen–nitrogen bonding. Tribromo-TIPS-diazatetracene delivered a 2D-brick wall structure with no sign of a halogen bonding. Dibromo-TIPS-tetracene crystallized neither in a herringbone nor in a brick wall motif. These results show that for halogenated azaacenes at least weak halogen–nitrogen interactions exist.

Theoretical investigations on electronic and charge transport properties of novel organic semiconductors – Triisopropylsilylethynyl(TIPS)-functionalized anthradifuran and anthradithiophene derivatives

Triisopropylsilylethynyl(TIPS)-functionalized polyacenes, a new family of novel organic semiconductors, have attracted extensive interests due to their high solubility, good air stability, and high performance in organic field effect transistors (OFETs). In present study, the electronic and charge transport properties of a series of chalcogen-doped TIPS-pentacene (PENT) derivatives have been studied by density functional theory (DFT). Their electronic structures, ionization energies, electron affinities, reorganization energies, transfer integrals of possible hopping pathways, hole and electron mobilities, and anisotropic mobilities have be calculated to discuss the role of various factors affecting the charge transport properties of these novel organic semiconductors. Fluorination and chlorination effects on the electronic properties and reorganization energies of the studied molecules have also been studied. The calculated results show that the fluorination and chlorination are efficient strategies for tuning the molecular orbital level to decrease the charge injection barrier from metal electrode and improve their oxidative stabilities. Though the fluorination indeed lowers the lowest unoccupied molecular orbital (LUMO) levels of TIPS-PENT derivatives, it also leads to much larger reorganization energies and smaller electron transfer integrals. Thus, it may be not an effective way for TIPS-PENT derivatives to convert a p-type semiconductor to an n-type one. Our calculated hole mobilities for available experiment crystal structures are in good agreement with the experimental observation. The computed hole mobilities for TIPS-anthradithiophene (ADT) and TIPS-teracenothiophene (TT) are 0.622 and 1.186cm2V−1s−1, respectively, which are in good agreement with the corresponding experimental values of 0.6 and 1.25cm2V−1s−1, respectively. Their relative calculated electron mobilities are 0.607 and 0.637cm2V−1s−1, respectively. The results show that they have high balanced hole and electron mobilities and may be promising candidates for ambipolar organic semiconductors. The studies on anisotropic mobilities of the selected derivatives show that they exhibit remarkable anisotropic behaviors and the hole and electron transfers along the parallel hopping pathway make the dominant contribution on their charge carrier mobilities.

A high molecular weight triisopropylsilylethynyl (TIPS)-benzodithiophene and diketopyrrolopyrrole-based copolymer for high performance organic photovoltaic cells

A high-molecular-weight conjugated polymer consisting of alternating TIPS-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT) and diketopyrrolo[3,4-c]pyrrole (DPP) was synthesized by Suzuki cross-coupling and characterized for use in high performance OPVs. Good structural order, self-assembly in spun-cast films, and carrier mobility were observed. PTIPSBDT–DPP showed an OFET hole mobility of up to 0.12 cm2 V−1 s−1. Power conversion efficiencies of up to 8.0% were demonstrated for OPV devices.

Triisopropylsilylethynyl‐Functionalized Graphene‐Like Fragment Semiconductors: Synthesis, Crystal Packing, and Density Functional Theory Calculations

Tri-isopropylsilylethynyl (TIPS)-functionalized polycyclic aromatic hydrocarbon (PAH) molecules incorporate structural components of graphene nanoribbons and represent a family of model molecules that form organic crystal semiconductors for electronic devices. Here, we report a series of TIPS-functionalized PAHs and discuss their electronic properties and crystal packing features. We observe that these soluble compounds easily form one-dimensional (1 D) packing arrangements and allow a direct evolution of the π stacking by varying the geometric shape. We find that the aspect ratio between length and width plays an important role on crystal packing. Our result indicates that when the PAH molecules have zigzag edges, these can provide enough volume for the molecules to rotate and reorient, alleviating the unfavorable electrostatic interactions found in perfectly cofacial π-π stacking. Density functional theory calculations were carried out to provide insights into how the molecular geometric shape influences the electronic structure and transport properties. The calculations indicate that, among the compounds studied here, "brick-layer" stacks provide the highest hole mobility.