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1.
Proc Natl Acad Sci U S A ; 117(30): 17551-17557, 2020 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-32647062

RESUMO

The rational creation of two-component conjugated polymer systems with high levels of phase purity in each component is challenging but crucial for realizing printed soft-matter electronics. Here, we report a mixed-flow microfluidic printing (MFMP) approach for two-component π-polymer systems that significantly elevates phase purity in bulk-heterojunction solar cells and thin-film transistors. MFMP integrates laminar and extensional flows using a specially microstructured shear blade, designed with fluid flow simulation tools to tune the flow patterns and induce shear, stretch, and pushout effects. This optimizes polymer conformation and semiconducting blend order as assessed by atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing incidence wide-angle X-ray scattering (GIWAXS), resonant soft X-ray scattering (R-SoXS), photovoltaic response, and field effect mobility. For printed all-polymer (poly[(5,6-difluoro-2-octyl-2H-benzotriazole-4,7-diyl)-2,5-thiophenediyl[4,8-bis[5-(2-hexyldecyl)-2-thienyl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]-2,5-thiophenediyl]) [J51]:(poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)}) [N2200]) solar cells, this approach enhances short-circuit currents and fill factors, with power conversion efficiency increasing from 5.20% for conventional blade coating to 7.80% for MFMP. Moreover, the performance of mixed polymer ambipolar [poly(3-hexylthiophene-2,5-diyl) (P3HT):N2200] and semiconducting:insulating polymer unipolar (N2200:polystyrene) transistors is similarly enhanced, underscoring versatility for two-component π-polymer systems. Mixed-flow designs offer modalities for achieving high-performance organic optoelectronics via innovative printing methodologies.

2.
Artigo em Inglês | MEDLINE | ID: mdl-32633937

RESUMO

Self-assembled nanodielectrics (SANDs) consist of alternating layers of polarized phosphonate-functionalized azastibazolium π-electron (PAE) and high-k dielectric metal oxide (ZrO2 or HfOx) films. SANDs are desirable gate dielectrics materials for thin-film transistor applications because of their excellent properties such as low-temperature fabrication, large dielectric strength, and large capacitance. In this paper, we investigate the cross-plane thermal boundary conductance of SANDs using the frequency domain thermoreflectance (FDTR) technique. First, we characterize the thermal conductance of PAE self-assembled monolayers (SAMs), inverted-PAE (IPAE) SAMs, and mixed PAE-IPAE SAMs, sandwiched between thin gold and silica (SiO2) films at the top and bottom surfaces. Next, we quantify the thermal conductance of SAND-n with different numbers (n) of PAE-ZrO2 layers and thicknesses ranging between 4.7 and 11.3 nm. From the FDTR measurements, we observe that the thermal boundary conductance of the SAMs can be tuned between 42.1 ± 4.6 MW/(m2 K) and 52.4 ± 2.5 MW/(m2 K), based on the relative density of the PAE and IPAE chromophores. In the SAND-n samples, we observe a monotonic decrease in the thermal conductance with increasing n. We use the measured thermal conductance data in a series resistance model to estimate a thermal interface conductance of 695 MW/(m2 K) for the contact between the PAE chromophore and the zirconium dioxide films, which is an order of magnitude larger than the SAMs. We attribute the improved thermal conductance to stronger adhesion between the PAE chromophore and the zirconium dioxide films, as compared to the weakly bonded SAMs to the gold and silicon dioxide films.

3.
J Am Chem Soc ; 2020 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-32698577

RESUMO

Emerging non-fullerene acceptors (NFAs) with crystalline domains enable high-performance bulk heterojunction (BHJ) solar cells. Thermal annealing is known to enhance BHJ photoactive layer morphology and performance. However, the microscopic mechanism of annealing-induced performance enhancement is poorly understood in emerging NFAs, espe-cially regarding competing factors. Here, optimized thermal annealing of the model system PBDB-TF:Y6 (Y6 = 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2",3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]-thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) decreases open circuit voltage (VOC) but increases the short circuit current (JSC) and fill factor (FF) such that the resulting power conversion efficiency (PCE) increases from 14% to 15% in ambient. Here we systematically investigate these thermal annealing effects through in-depth characteri-zations of carrier mobility, film morphology, charge photogeneration and recombination, using SCLC, GIXRD, AFM, XPS, NEXAFS, R-SoXS, TEM, STEM, fs/ns TA spectroscopy, 2DES, and impedance spectroscopy. Surprisingly, thermal annealing does not alter film crystallinity, nor R-SoXS characteristic size scale, relative average phase purity, nor TEM-imaged phase separation, but rather facilitates Y6 migration to the BHJ film top surface, changes the PBDB-TF/Y6 vertical phase separa-tion and intermixing, and reduces bottom surface roughness. While these morphology changes increase bimolecular re-combination (BR) and lower the free charge (FC) yield, they also increase the average of electron and hole mobility by at least two-fold. Importantly, the increased µh dominates and underlies the increased FF and PCE. Single-crystal X-ray diffraction reveals that Y6 molecules co-facially pack via their end-groups/cores, with the shortest π-π distance as close as 3.34 Å, clarifying out-of-plane π-face-on molecular orientation in the nano-crystalline BHJ domains. DFT analysis of Y6 crystals reveals hole/electron re-organization energies as low as 160/150 meV, large intermolecular electronic coupling integrals of 12.1 - 37.9 meV, ra-tionalizing the 3D electron transport and relatively high µe of 10-4 cm2 V-1 s-1. Taken all together, this work clarifies the richness of thermal annealing effects in high-efficiency NFA solar cells and tasks for future materials design.

4.
Artigo em Inglês | MEDLINE | ID: mdl-32703807

RESUMO

The field-effect electron mobility of aqueous solution-processed indium gallium oxide (IGO) thin-film transistors (TFTs) is significantly enhanced by polyvinyl alcohol (PVA) addition to the precursor solution, a >70-fold increase to 7.9 cm2/Vs. To understand the origin of this remarkable phenomenon, microstructure, electronic structure, and charge transport of IGO:PVA film are investigated by a battery of experimental and theoretical techniques, including In K-edge and Ga K-edge extended X-ray absorption fine structure (EXAFS); resonant soft X-ray scattering (R-SoXS); ultraviolet photoelectron spectroscopy (UPS); Fourier transform-infrared (FT-IR) spectroscopy; time-of-flight secondary-ion mass spectrometry (ToF-SIMS); composition-/processing-dependent TFT properties; high-resolution solid-state 1H, 71Ga, and 115In NMR spectroscopy; and discrete Fourier transform (DFT) analysis with ab initio molecular dynamics (MD) liquid-quench simulations. The 71Ga{1H} rotational-echo double-resonance (REDOR) NMR and other data indicate that PVA achieves optimal H doping with a Ga···H distance of ∼3.4 Å and conversion from six- to four-coordinate Ga, which together suppress deep trap defect localization. This reduces metal-oxide polyhedral distortion, thereby increasing the electron mobility. Hydroxyl polymer doping thus offers a pathway for efficient H doping in green solvent-processed metal oxide films and the promise of high-performance, ultra-stable metal oxide semiconductor electronics with simple binary compositions.

5.
J Am Chem Soc ; 2020 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-32539371

RESUMO

The frequency-dependent capacitance of low-temperature solution-processed metal oxide (MO) dielectrics typically yields unreliable and unstable thin-film transistor (TFT) performance metrics, which hinders the development of next-generation roll-to-roll MO electronics and obscures intercomparisons between processing methodologies. Here, capacitance values stable over a wide frequency range are achieved in low-temperature combustion-synthesized aluminum oxide (AlOx) dielectric films by fluoride doping. For an optimal F incorporation of ∼3.7 atomic % F, the F:AlOx film capacitance of 166 ± 11 nF/cm2 is stable over a 10-1-104 Hz frequency range, far more stable than that of neat AlOx films (capacitance = 336 ± 201 nF/cm2) which falls from 781 ± 85 nF/cm2 to 104 ± 4 nF/cm2 over this frequency range. Importantly, both n-type/inorganic and p-type/organic TFTs exhibit reliable electrical characteristics with minimum hysteresis when employing the F:AlOx dielectric with ∼3.7 atomic % F. Systematic characterization of film microstructural/compositional and electronic/dielectric properties by X-ray photoelectron spectroscopy, time-of-fight secondary ion mass spectrometry, cross-section transmission electron microscopy, solid-state nuclear magnetic resonance, and UV-vis absorption spectroscopy reveal that fluoride doping generates AlOF, which strongly reduces the mobile hydrogen content, suppressing polarization mechanisms at low frequencies. Thus, this work provides a broadly applicable anion doping strategy for the realization of high-performance solution-processed metal oxide dielectrics for both organic and inorganic electronics applications.

6.
Nat Commun ; 11(1): 2405, 2020 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-32415064

RESUMO

Fiber-based electronics enabling lightweight and mechanically flexible/stretchable functions are desirable for numerous e-textile/e-skin optoelectronic applications. These wearable devices require low-cost manufacturing, high reliability, multifunctionality and long-term stability. Here, we report the preparation of representative classes of 3D-inorganic nanofiber network (FN) films by a blow-spinning technique, including semiconducting indium-gallium-zinc oxide (IGZO) and copper oxide, as well as conducting indium-tin oxide and copper metal. Specifically, thin-film transistors based on IGZO FN exhibit negligible performance degradation after one thousand bending cycles and exceptional room-temperature gas sensing performance. Owing to their great stretchability, these metal oxide FNs can be laminated/embedded on/into elastomers, yielding multifunctional single-sensing resistors as well as fully monolithically integrated e-skin devices. These can detect and differentiate multiple stimuli including analytes, light, strain, pressure, temperature, humidity, body movement, and respiratory functions. All of these FN-based devices exhibit excellent sensitivity, response time, and detection limits, making them promising candidates for versatile wearable electronics.

7.
J Am Chem Soc ; 142(17): 8019-8028, 2020 Apr 29.
Artigo em Inglês | MEDLINE | ID: mdl-32250115

RESUMO

Tris[N,N-bis(trimethylsilyl)amide]lanthanum (LaNTMS) is an efficient and selective homogeneous catalyst for the deoxygenative reduction of tertiary and secondary amides with pinacolborane (HBpin) at mild temperatures (25-60 °C). The reaction, which yields amines and O(Bpin)2, tolerates nitro, halide, and amino functional groups well, and this amide reduction is completely selective, with the exclusion of both competing inter- and intramolecular alkene/alkyne hydroboration. Kinetic studies indicate that amide reduction obeys an unusual mixed-order rate law which is proposed to originate from saturation of the catalyst complex with HBpin. Kinetic and thermodynamic studies, isotopic labeling, and DFT calculations using energetic span analysis suggest the role of a [(Me3Si)2N]2La-OCHR(NR'2)[HBpin] active catalyst, and hydride transfer is proposed to be ligand-centered. These results add to the growing list of transformations that commercially available LaNTMS is competent to catalyze, further underscoring the value and versatility of lanthanide complexes in homogeneous catalysis.

8.
J Am Chem Soc ; 2020 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-32053356

RESUMO

Mechanically flexible films of the highly crystalline core-cyanated perylenediimide (PDIF-CN2) molecular semiconductor are achieved via a novel grain boundary plasticization strategy in which a specially designed polymeric binder (PB) is used to connect crystallites at the grain boundaries. The new PB has a naphthalenediimide-dithiophene π-conjugated backbone end-functionalized with PDI units. In contrast to conventional polymer-small molecule blends where distinct phase separation occurs, this blend film with plasticized grain boundaries exhibits a morphology typical of homogeneous PDIF-CN2 films which is preserved upon bending at radii as small as 2 mm. Thin-film transistors fabricated with PB/PDIF-CN2 blends exhibit substantial electron mobilities even after repeated bending. This design represents a new approach to realizing flexible and textured semiconducting π-electron films with good mechanical and charge transport properties.

9.
ACS Nano ; 2020 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-32078300

RESUMO

Layered indium selenide (InSe) is an emerging two-dimensional semiconductor that has shown significant promise for high-performance transistors and photodetectors. The range of optoelectronic applications for InSe can potentially be broadened by forming mixed-dimensional van der Waals heterostructures with zero-dimensional molecular systems that are widely employed in organic electronics and photovoltaics. Here, we report the spatially resolved investigation of photoinduced charge separation between InSe and two molecules (C70 and C8-BTBT) using scanning tunneling microscopy combined with laser illumination. We experimentally and computationally show that InSe forms type-II and type-I heterojunctions with C70 and C8-BTBT, respectively, due to an interplay of charge transfer and dielectric screening at the interface. Laser-excited scanning tunneling spectroscopy reveals a ∼0.25 eV decrease in the energy of the lowest unoccupied molecular orbital of C70 with optical illumination. Furthermore, photoluminescence spectroscopy and Kelvin probe force microscopy indicate that electron transfer from InSe to C70 in the type-II heterojunction induces a photovoltage that quantitatively matches the observed downshift in the tunneling spectra. In contrast, no significant changes are observed upon optical illumination in the type-I heterojunction formed between InSe and C8-BTBT. Density functional theory calculations further show that, despite the weak coupling between the molecular species and InSe, the band alignment of these mixed-dimensional heterostructures strongly differs from the one suggested by the ionization potential and electronic affinities of the isolated components. Self-energy-corrected density functional theory indicates that these effects are the result of the combination of charge redistribution at the interface and heterogeneous dielectric screening of the electron-electron interactions in the heterostructure. In addition to providing specific insight for mixed-dimensional InSe-organic van der Waals heterostructures, this work establishes a general experimental methodology for studying localized charge transfer at the molecular scale that is applicable to other photoactive nanoscale systems.

10.
Artigo em Inglês | MEDLINE | ID: mdl-31986236

RESUMO

Introducing polar functional groups into widely used polyolefins can enhance polymer surface, rheological, mixing, and other properties, potentially upgrading polyolefins for advanced, value-added applications. The metal catalyst-mediated copolymerization of non-polar olefins with polar comonomers represents the seemingly most straightforward, atom- and energy-efficient approach for synthesizing polar functionalized polyolefins. However, electrophilic early transition metal (groups 3 and 4)-catalyzed processes which have achieved remarkable success in conventional olefin polymerizations, encounter severe limitations here, largely associated with the Lewis basicity of the polar co-monomers. In recent years, however, new catalytic systems have been developed and successful strategies have emerged. In this Minireview, we summarize the recent progress in early transition metal polymerization catalyst development, categorized by the catalytic metal complex and polar comonomer identity. Furthermore, we discuss advances in the mechanistic understanding of these polymerizations, focusing on critical challenges and strategies that mitigate them.

11.
Nanoscale ; 12(4): 2715-2725, 2020 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-31950961

RESUMO

Multi-component 3D porous structures are highly promising hierarchical materials for numerous applications. Herein we show that atomic-layer deposition (ALD) of MoS2 on graphene foams with variable pore size is a promising methodology to prepare complex 3D heterostructures to be used as electrocatalysts for the hydrogen evolution reaction (HER). The effect of MoS2 crystallinity is studied and a trade-off between the high density of defects naturally presented in amorphous MoS2 coatings and the highly crystalline phase obtained after annealing at 800 °C is established. Specifically, an optimal annealing at 500 °C is shown to yield improved catalytic performance with an overpotential of 180 mV, a low Tafel slope of 47 mV dec-1, and a high exchange current of 17 µA cm-2. The ALD deposition is highly conformal, and thus advantageous when coating 3D porous structures with small pore sizes, as required for real-world applications. This approach is enabled by conformal thin film deposition on porous structures with controlled crystallinity by tuning the annealing temperature. The results presented here therefore serve as an effective and general platform for the design of chemically and structurally tunable, binder-free, complex, lightweight, and highly efficient 3D porous heterostructures to be used for catalysis, energy storage, composite materials, sensors, water treatment, and more.

12.
Nano Lett ; 19(12): 8956-8963, 2019 12 11.
Artigo em Inglês | MEDLINE | ID: mdl-31682761

RESUMO

Coherence is a significant factor in nanoscale electronic insulator technology and necessitates an understanding of the structure-property relationship between constructive and destructive quantum interference. This is particularly important in organic dielectric circuitry, which is the subject of this work. It is known that molecular wires composed of (i) meta-substituted phenylene rings, (ii) cross-conjugated double bonds (orthogonal to the molecular long axis), and (iii) single bonds can dramatically reduce electrical transmission. Here we add to these tools the use of an unexplored molecular shape to create strong and counterintuitive interference: a fully conjugated molecular wire with a structure that is forced back on itself in a Z shape, thereby exhibiting remarkably low conductance (G = 0.43 × 10-9 S) even though the phenylene arrangements are ortho- rather than meta-disposed. We call these Z-shaped molecules having ultralow conduction Z-ortho-regio-resistive organics (ZORROs). Here we analyze a series of ZORRO molecules and find them to have significant insulating properties in the coherent electron-transport regime due to interfering transmission pathways in the phenylene rings. Importantly, we find that both electron-withdrawing (fluorine) and electron-donating (methoxy) substituents enhance the transmission, which is not desirable. The former is due to the suppression of the destructive quantum interference at the F site, thereby enhancing the overall transmission, much like a Büttiker probe. The latter is due to a methoxy unit resonance additive effect, akin to oxygen doping, and positively contributes to the transmission. We then examine the effects of replacing the phenylene rings with 4,5- and 3,4-disubstituted thiophenes and how this ZORRO modification further reduces the transmission. An ultralow conductance of 0.13 × 10-9 S and a relatively high dielectric constant (εr) of ∼5 are predicted for the 3,4-thiophene ZORRO derivative, which closely resembles two cross-conjugated units, making it an intriguing candidate for a gate dielectric material.

13.
Chemphyschem ; 20(20): 2608-2626, 2019 10 16.
Artigo em Inglês | MEDLINE | ID: mdl-31529569

RESUMO

Accurate single-crystal X-ray diffraction data offer a unique opportunity to compare and contrast the atomistic details of bulk heterojunction photovoltaic small-molecule acceptor structure and packing, as well as provide an essential starting point for computational electronic structure and charge transport analysis. Herein, we report diffraction-derived crystal structures and computational analyses on the n-type semiconductors which enable some of the highest efficiency organic solar cells produced to date, 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC) and seven derivatives (including three new crystal structures: 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-propylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC-C3), 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(3-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (m-ITIC-C6), and 3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-butylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC-C4-4F). IDTT acceptors typically pack in a face-to-face fashion with π-π distances ranging from 3.28-3.95 Å. Additionally, edge-to-face packing is observed with S⋯π interactions as short as 3.21-3.24 Å. Moreover, ITIC end group identities and side chain substituents influence the nature and strength of noncovalent interactions (e. g. H-bonding, π-π) and thus correlate with the observed packing motif, electronic structure, and charge transport properties of the crystals. Density functional theory (DFT) calculations reveal relatively large nearest-neighbor intermolecular π-π electronic couplings (5.85-56.8 meV) and correlate the nature of the band structure with the dispersion interactions in the single crystals and core-end group polarization effects. Overall, this combined experimental and theoretical work reveals key insights into crystal engineering strategies for indacenodithienothiophene (IDTT) acceptors, as well as general design rules for high-efficiency post-fullerene small molecule acceptors.

14.
Adv Mater ; 31(40): e1903239, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31402528

RESUMO

Recent perovskite solar cell (PSC) advances have pursued strategies for reducing interfacial energetic mismatches to mitigate energy losses, as well as to minimize interfacial and bulk defects and ion vacancies to maximize charge transfer. Here nonconjugated multi-zwitterionic small-molecule electrolytes (NSEs) are introduced, which act not only as charge-extracting layers for barrier-free charge collection at planar triple cation PSC cathodes but also passivate charged defects at the perovskite bulk/interface via a spontaneous bottom-up passivation effect. Implementing these synergistic properties affords NSE-based planar PSCs that deliver a remarkable power conversion efficiency of 21.18% with a maximum VOC = 1.19 V, in combination with suppressed hysteresis and enhanced environmental, thermal, and light-soaking stability. Thus, this work demonstrates that the bottom-up, simultaneous interfacial and bulk trap passivation using NSE modifiers is a promising strategy to overcome outstanding issues impeding further PSC advances.

15.
ChemSusChem ; 2019 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-31464059

RESUMO

Efficient conversion of renewable biomass platform chemicals into high-quality fuels remains challenging. A one-pot catalytic approach has been developed to synthesize various structurally defined biofuels by using Hf(OTf)4 and Pd/C for selective tandem catalysis and 2-methylfuran (2-MF) as a renewable feedstock. 2-MF first undergoes Lewis acid-catalyzed hydroxyalkylation/alkylation (HAA) condensation with carbonyl compounds to afford intermediates containing the targeted carbon skeletons of hydrocarbon or ether products, and these intermediates then undergo hydrogenation or hydrodeoxygenation to afford the target products, catalyzed by metal triflate+Pd/C in the same pot. The present process can produce structurally defined alkanes and cyclic ethers under mild conditions.

16.
J Am Chem Soc ; 141(34): 13410-13420, 2019 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-31379156

RESUMO

Achieving efficient polymer solar cells (PSCs) requires a structurally optimal donor-acceptor heterojunction morphology. Here we report the combined experimental and theoretical characterization of a benzodithiophene-benzothiadiazole donor polymer series (PBTZF4-R; R = alkyl substituent) blended with the non-fullerene acceptor ITIC-Th and analyze the effects of substituent dimensions on blend morphology, charge transport, carrier dynamics, and PSC metrics. Varying substituent dimensions has a pronounced effect on the blend morphology with a direct link between domain purity, to some extent domain dimensions, and charge generation and collection. The polymer with the smallest alkyl substituent yields the highest PSC power conversion efficiency (PCE, 11%), reflecting relatively small, high-purity domains and possibly benefiting from "matched" donor polymer-small molecule acceptor orientations. The distinctive morphologies arising from the substituents are investigated using molecular dynamics (MD) simulations which reveal that substituent dimensions dictate a well-defined set of polymer conformations, in turn driving chain aggregation and, ultimately, the various film morphologies and mixing with acceptor small molecules. A straightforward energetic parameter explains the experimental polymer domain morphological trends, hence PCE, and suggests strategies for substituent selection to optimize PSC materials morphologies.

17.
Acc Chem Res ; 52(5): 1428-1438, 2019 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-31038918

RESUMO

Materials with large nonlinear optical (NLO) response have the ability to manipulate the frequency and phase of incident light and exhibit phenomena that form the basis of modern telecommunication systems. In molecule-based materials, the second- and third-order NLO performance is related to the hyperpolarizability (ß) and second hyperpolarizability (γ) of the constituent molecules. The search for higher ß materials is driven by the desire to keep pace with expanding demand for high speed data transmission, while discovery of high γ chromophores is crucial for the development of emergent photonic technologies reliant on manipulation of "light-with-light". For decades, it was believed that for highest performance, organic NLO materials must be composed of planar π-system chromophores, and much exploratory research focused on subtle molecular modifications, which generally yielded incremental increases in µß, where µ is the molecular dipole moment. The surprising recent discovery that twisted π-system chromophores can exhibit dramatically higher ß values than their planar analogues has revealed a new design paradigm and stimulated the development of high performance twisted intramolecular charge transfer (TICT) chromophores, which are composed of electron-donating and electron-accepting π-substituents joined by a sterically constrained twisted biaryl fragment. In such chromophores, the twisting of the π-system enforces charge separation in the electronic ground state, leading to large dipole moments and low-lying charge-transfer excitations. This unique electronic structure forms the basis for enhanced NLO response, with an archetypal TICT chromophore, TMC-2, exhibiting very large second- ( µß = 24 000 × 10-48 esu) and third-order (γ = 1.4 × 10-33 esu) metrics in dilute low-polarity solutions. This Account summarizes several approaches to enhance µß in various environments, including (1) manipulating the biaryl torsional angle, (2) modifying the electron accepting fragment, (3) extending conjugation, (4) adding multiple twisted fragments, (5) modifying chromophore side chains, and (6) tuning the chromophore environment. Another set of modifications is explored to enhance γ, including (1) coupling to a cyanine dye to hybridize the cyanine and TICT orbitals, (2) manipulating the donor and acceptor group identity. The extensive modifications described above yield a detailed understanding of TICT chromophore molecular NLO response and unambiguous evidence that such chromophores have the potential to revolutionize organic electro-optics.

18.
J Am Chem Soc ; 141(19): 7822-7830, 2019 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-31017398

RESUMO

Recent decades have witnessed intense research efforts aimed at developing new homogeneous olefin polymerization catalysts, with a primary focus on metal-Cl or metal-hydrocarbyl precursors. Curiously, metal-NR2 precursors have received far less attention. In this contribution, the Zr-amido complex FI2ZrX2 (FI = 2,4-di- tert-butyl-6-((isobutylimino)methyl)phenolate, X = NMe2) is found to exhibit high ethylene polymerization activity and relatively high 1-octene coenchainment selectivity (up to 7.2 mol%) after sequential activation with trimethylaluminum, then Ph3C+B(C6F5)4-. In sharp contrast, catalysts with traditional hydrocarbyl ligands such as benzyl and methyl give low 1-octene incorporation (0-1.0 mol%). This unexpected selectivity persists under scaled/industrial operating conditions and was previously inaccessible with traditional metal-Cl or -hydrocarbyl precursors. NMR, X-ray diffraction, and catalytic control experiments indicate that in this case an FI ligand is abstracted from FI2Zr(NMe2)2 by trimethylaluminum in the activation process to yield a catalytically active cationic mono-FIZr species. Heretofore this process was believed to serve only as a major catalyst deactivation pathway to be avoided. This work demonstrates the importance of investigating diverse precatalyst monodentate σ-ligands in developing new catalyst systems, especially for group 4 olefin polymerization catalysts.

19.
Proc Natl Acad Sci U S A ; 116(19): 9230-9238, 2019 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-31004056

RESUMO

Metal oxide (MO) semiconductor thin films prepared from solution typically require multiple hours of thermal annealing to achieve optimal lattice densification, efficient charge transport, and stable device operation, presenting a major barrier to roll-to-roll manufacturing. Here, we report a highly efficient, cofuel-assisted scalable combustion blade-coating (CBC) process for MO film growth, which involves introducing both a fluorinated fuel and a preannealing step to remove deleterious organic contaminants and promote complete combustion. Ultrafast reaction and metal-oxygen-metal (M-O-M) lattice condensation then occur within 10-60 s at 200-350 °C for representative MO semiconductor [indium oxide (In2O3), indium-zinc oxide (IZO), indium-gallium-zinc oxide (IGZO)] and dielectric [aluminum oxide (Al2O3)] films. Thus, wafer-scale CBC fabrication of IGZO-Al2O3 thin-film transistors (TFTs) (60-s annealing) with field-effect mobilities as high as ∼25 cm2 V-1 s-1 and negligible threshold voltage deterioration in a demanding 4,000-s bias stress test are realized. Combined with polymer dielectrics, the CBC-derived IGZO TFTs on polyimide substrates exhibit high flexibility when bent to a 3-mm radius, with performance bending stability over 1,000 cycles.

20.
ACS Appl Mater Interfaces ; 11(24): 21424-21434, 2019 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-31014067

RESUMO

The design of a dye-sensitized solar cell (DSSC) based on the simultaneous incorporation of multiple dyes is examined. By investigating the use of the porphyrin-based YD2-o-C8 and YDD6, and the organic chromophore TTAR, which can act as complementary absorbers, we are able to enhance the capture of incoming light across the solar spectrum. This is demonstrated first by using a conventional DSSC architecture with a liquid electrolyte and performed a power conversion efficiency (PCE) of 11.2%, representing an improvement over cells based on each of the independent dyes. Next, we used Cs2SnI6 as an encapsulating layer over the sensitizing molecules to reduce charge leakage across the dye layers and also added to the absorption of longer wavelengths up to one micron. Finally, we fabricated a cell utilizing a Cs2SnI6/succinonitrile solid hole-transport electrolyte and achieved a PCE of ∼8.5%. It is expected that the all solid-state design will go a long way toward improving long-term device stability.

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