Publications by authors named "Qingshuo Wei"

18 Publications

  • Page 1 of 1

Outstanding Electrode-Dependent Seebeck Coefficients in Ionic Hydrogels for Thermally Chargeable Supercapacitor near Room Temperature.

ACS Appl Mater Interfaces 2020 Sep 16;12(39):43674-43683. Epub 2020 Sep 16.

Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.

Thermoelectric power generation from waste heat is an important component of future sustainable development. Ion-conducting materials are promising candidates because of their high Seebeck coefficients. This study demonstrates that ionic hydrogels based on imidazolium chloride salts exhibit outstanding Seebeck coefficients of up to 10 mV K. Along with their relatively high ionic conductivities (1.6 mS cm) and extremely low thermal conductivities (∼0.2 W m K), these hydrogels have good potential for use in heat recovery systems. The voltage behavior in response to temperature difference (stable or transient) differs significantly depending on the metal electrode material. We evaluated the electrode-dependent temperature sensitivity of the double layer capacitance of these hydrogels, which revealed that the thermally induced polarization of ions at the interface is one of the main contributors to the thermovoltage. Our results demonstrate the potential capability for ion and metal interactions to be used as an effective baseline for exploring ionic thermoelectric materials and devices. The developed thermoelectric supercapacitor exhibits reversible charging-discharging behavior under repeated disconnecting-connecting of an external load with a constant temperature difference, which offers a novel strategy for heat-to-electricity energy conversion from steady-temperature heat sources.
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http://dx.doi.org/10.1021/acsami.0c11752DOI Listing
September 2020

Reversible Protonic Doping in Poly(3,4-Ethylenedioxythiophene).

Polymers (Basel) 2018 Sep 25;10(10). Epub 2018 Sep 25.

Nanomaterials Research Institute, Department of Materials and Chemistry, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Japan.

In this study, poly(3,4-ethylenedioxythiophene), a benchmark-conducting polymer, was doped by protons. The doping and de-doping processes, using protonic acid and a base, were fully reversible. We predicted possible doping sites along the polymer chain using density functional theory (DFT) calculations. This study sheds potential light and understanding on the molecular design of highly conductive organic materials.
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http://dx.doi.org/10.3390/polym10101065DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6404222PMC
September 2018

Moisture-responsive supramolecular nanotubes.

Nanoscale 2018 Nov;10(43):20321-20328

Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.

Living organisms have evolved functional structures for seeds dispersal in response to humidity changes. In this study, we construct moisture-responsive nanotubes by the supramolecular coordination of a peptide lipid with metal ions for potential applications in material delivery systems. These hydrophilic nanotubes can uptake atmospheric moisture and the water molecules are associated with unsaturated metal centers of the bis(lipid)-metal(ii) complex, thereby changing the molecular packing and inducing morphological transformation from nanotubes to sheets. The moisture responsivity of nanotubes depends on the hydration behavior of the metal ions. Co(ii)-coordinated nanotube shows higher moisture responsivity than that of the Zn(ii)-coordinated one since Co(ii) ion has stronger association with water molecules. These two nanotubes are self-assembled by the same molecular packings; however, they show different mechanisms in morphological changes. The Co(ii)-coordinated nanotube transforms into a sheet accompanied with the destruction of the complex and reverse molecular packing, whereas Zn(ii)-coordinated nanotube transforms into a sheet with a change in the complex geometry. Further, the Co(ii)-coordinated nanotubes exhibit reversible morphological changes between nanotubes and sheets, while Zn(ii)-coordinated nanotubes exhibit a one-way morphological change. These nanotubes also show potential applications in the release of fragrance oil under high humidity environments.
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http://dx.doi.org/10.1039/c8nr05748fDOI Listing
November 2018

Photoinduced Dedoping of Conducting Polymers: An Approach to Precise Control of the Carrier Concentration and Understanding Transport Properties.

ACS Appl Mater Interfaces 2016 Jan 15;8(3):2054-60. Epub 2016 Jan 15.

Nanomaterials Research Institute, Department of Materials and Chemistry, National Institute of Advanced Industrial Science and Technology , 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan.

Exploring the various applications of conjugated polymers requires systematic studies of their physical properties as a function of the doping density, which, consequently, calls for precise control of their doping density. In this study, we report a novel solid-state photoinduced charge-transfer reaction that dedopes highly conductive polyelectrolyte complexes such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate). Varying the UV-irradiation time of this material allows the carrier density inside the film to be precisely controlled over more than 3 orders of magnitude. We extract the carrier density, carrier mobility, and Seebeck coefficient at different doping levels to obtain a clear image of carrier-transport mechanisms. This approach not only leads to a better understanding of the physical properties of the conducting polymer but also is useful for developing applications requiring patterned, large-area conducting polymers.
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http://dx.doi.org/10.1021/acsami.5b10453DOI Listing
January 2016

Recent Progress on PEDOT-Based Thermoelectric Materials.

Materials (Basel) 2015 Feb 16;8(2):732-750. Epub 2015 Feb 16.

Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan.

The thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT)-based materials have attracted attention recently because of their remarkable electrical conductivity, power factor, and figure of merit. In this review, we summarize recent efforts toward improving the thermoelectric properties of PEDOT-based materials. We also discuss thermoelectric measurement techniques and several unsolved problems with the PEDOT system such as the effect of water absorption from the air and the anisotropic thermoelectric properties. In the last part, we describe our work on improving the power output of thermoelectric modules by using PEDOT, and we outline the potential applications of polymer thermoelectric generators.
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http://dx.doi.org/10.3390/ma8020732DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5455279PMC
February 2015

Line patterns from cylinder-forming photocleavable block copolymers.

Adv Mater 2013 Sep 19;25(34):4690-5. Epub 2013 Jul 19.

Department of Polymer Science and Engineering, 120 Governors Drive, University of Massachusetts, Amherst, MA 01003, USA.

A robust route for the preparation of nanoscopic line patterns from polystyrene-block-poly(ethylene oxide) featuring a photocleavable o-nitrobenzyl ester junction is demonstrated. After mild UV (λ = 365 nm) exposure and selective removal of the PEO microdomains, the polymer trench patterns are used as scaffold to fabricate highly ordered arrays of silica or Au line patterns.
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http://dx.doi.org/10.1002/adma.201301556DOI Listing
September 2013

Morphological change and mobility enhancement in PEDOT:PSS by adding co-solvents.

Adv Mater 2013 May 19;25(20):2831-6. Epub 2013 Apr 19.

Nanosystem Research Institute, National Institute of Advanced Industrial, Science and Technology, 1-2-1 Namiki, Tsukuba, Ibaraki, Japan.

Adding ethylene glycol (EG) to a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solution improves the crystallinity of the PEDOT and the ordering of the PEDOT nanocrystals in solid films. The carrier-mobility enhancement is confirmed by using ion-gel transistors combined with in situ UV-vis-NIR spectroscopy.
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http://dx.doi.org/10.1002/adma.201205158DOI Listing
May 2013

Flexible low-voltage polymer thin-film transistors using supercritical CO2-deposited ZrO2 dielectrics.

ACS Appl Mater Interfaces 2012 May 1;4(5):2322-4. Epub 2012 May 1.

Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Drive, Amherst, Massachusetts 01003, USA.

The fabrication of low-voltage flexible organic thin film transistors using zirconia (ZrO(2)) dielectric layers prepared via supercritical fluid deposition was studied. Continuous, single-phase films of approximately 30 nm thick ZrO(2) were grown on polyimide (PI)/aluminum (Al) substrates at 250 °C via hydrolysis of tetrakis(2,2,6,6-tetramethyl-3,5-heptane-dionato) zirconium in supercritical carbon dioxide. This dielectric layer showed a high areal capacitance of 317 nF cm(-2) at 1 kHz and a low leakage current of 1.8 × 10(-6) A cm(-2) at an applied voltage of -3 V. By using poly(3-hexylthiophene) (P3HT) as a semiconductor, we have fabricated flexible thin film transistors operating at V(DS) = -0.5 V and V(G) in a range from 0.5 V to -4 V, with on/off ratios on the order of 1 × 10(3) and mobility values higher than 0.1 cm(2)/(V s).
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http://dx.doi.org/10.1021/am300371dDOI Listing
May 2012

Interfacial modification of organic photovoltaic devices by molecular self-organization.

Phys Chem Chem Phys 2012 Mar 9;14(11):3713-24. Epub 2012 Feb 9.

Department of Applied Chemistry, School of Engineering, The University of Tokyo, Tokyo, Japan.

This feature article focuses on the relationship between the interfacial structures constructed by molecular self-organization and the properties of organic photovoltaic devices. The use of self-assembled monolayers (SAMs) is reviewed for metal and metal oxide/organic interfaces, while surface-segregated monolayers (SSMs) are introduced as a new method for the modification of organic/organic interfaces. Research up to now has clearly demonstrated the effectiveness of the control of energy levels and other properties at the interfaces to enhance photovoltaic performance. The possibility of more precise control of the interfacial structures is also discussed.
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http://dx.doi.org/10.1039/c2cp40198cDOI Listing
March 2012

Effects of block length in copolymers based on regioregular oligothiophenes linked with electron-accepting units.

Macromol Rapid Commun 2012 Apr 9;33(8):658-63. Epub 2012 Feb 9.

Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

Copolymers with an alternating structure of regioregular oligo(3-hexylthiophene) (O3HT) with different lengths and 2,5-dibutyl-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) were synthesized through Stille coupling reaction. The light absorption of the copolymers can be rationally tuned to have a broad spectrum across the visible region by adjusting the length of O3HT. Organic solar cells fabricated with the copolymers and PCBM showed a broad photoresponse and a comparable efficiency to that of poly(3-hexylthiophene) (P3HT):PCBM cells. The external quantum efficiency and fluorescence spectra suggested that the intrachain energy transfer from the O3HT block to the vicinity of the DPP unit could limit the photovoltaic performance of the copolymers.
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http://dx.doi.org/10.1002/marc.201100827DOI Listing
April 2012

Additive-driven assembly of block copolymer-nanoparticle hybrid materials for solution processable floating gate memory.

ACS Nano 2012 Feb 30;6(2):1188-94. Epub 2012 Jan 30.

Department of Polymer Science and Engineering, University of Massachusetts-Amherst, 120 Governors Drive, Amherst, Massachusetts 01003, United States.

Floating gate memory devices were fabricated using well-ordered gold nanoparticle/block copolymer hybrid films as the charge trapping layers, SiO(2) as the dielectric layer, and poly(3-hexylthiophene) as the semiconductor layer. The charge trapping layer was prepared via self-assembly. The addition of Au nanoparticles that selectively hydrogen bond with pyridine in a poly(styrene-b-2-vinyl pyridine) block copolymer yields well-ordered hybrid materials at Au nanoparticle loadings up to 40 wt %. The characteristics of the memory window were tuned by simple control of the Au nanoparticle concentration. This approach enables the fabrication of well-ordered charge storage layers by solution processing, which is extendable for the fabrications of large area and high density devices via roll-to-roll processing.
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http://dx.doi.org/10.1021/nn203847rDOI Listing
February 2012

Independent Tuning of the Band Gap and Redox Potential of Graphene Quantum Dots.

J Phys Chem Lett 2011 May 22;2(10):1119-24. Epub 2011 Apr 22.

†Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States.

The band gap and redox potential of semiconductor nanocrystals are two quantities of primary importance for their applications in energy conversion devices. Herein, we report on covalent functionalization of colloidal graphene quantum dots through a solution-chemistry approach and studies of their band gaps and redox potentials. We show that their band gaps and redox potentials can be independently controlled, the former by size and the latter by functionalization. The size and the functionalization dependence of the properties can be numerically reproduced with tight-binding calculations, which thus provides a simple theoretical tool to guide the design of graphene QDs with desired properties.
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http://dx.doi.org/10.1021/jz200450rDOI Listing
May 2011

Tailoring organic heterojunction interfaces in bilayer polymer photovoltaic devices.

Nat Mater 2011 Jun 15;10(6):450-5. Epub 2011 May 15.

Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-8656, Japan.

In an ideal model, a p-n junction is formed by two stacked slabs of semiconductors. Although the construction of actual devices is generally more complex, we show that such a simple method can in fact be applied to the formation of organic heterojunctions. Two films of the organic semiconductors poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) can be connected by a simple film-transfer method without disturbing their flat surfaces. Each film can further be modified with a surface-segregated monolayer to tune the strength and direction of the surface dipole moment. Using this method, we fabricated bilayer organic photovoltaic devices with interfacial dipole moments that were selected to align the energy levels at the heterojunction. The open-circuit voltages of the P3HT/PCBM devices could be tuned over a wide range between 0.3 and 0.95 V, indicating that, even if the same combination of bulk materials is used, the interfacial properties drastically alter the performance of organic photovoltaic devices.
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http://dx.doi.org/10.1038/nmat3026DOI Listing
June 2011

All-polymer solar cells from perylene diimide based copolymers: material design and phase separation control.

Angew Chem Int Ed Engl 2011 Mar 21;50(12):2799-803. Epub 2011 Feb 21.

HASHIMOTO Light Energy Conversion Project, Exploratory Research for Advanced Technology, Japan.

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http://dx.doi.org/10.1002/anie.201005408DOI Listing
March 2011

Experimental investigation of charge carrier transport in organic thin-film transistors with "buried surface layers".

ACS Appl Mater Interfaces 2011 Feb 27;3(2):139-42. Epub 2011 Jan 27.

We studied how the layers with different transport properties buried inside a semiconductor material affect the characteristics of organic thin film transistors (OTFT) using a well-defined multilayered structure fabricated by a contact film transfer method that we recently developed (ACS Appl. Mater. Interfaces 1, 2660 (2009)). A simple model with the charge distribution in the organic semiconductor film, the mobility dependence on the charge density, and the buried surface layers with a high mobility successfully reproduced the experimental mobility dependence on the thickness of the spin-coated films and the gate voltage. These results demonstrated that charge transport layers located far from the dielectric interface could contribute significantly to the total current in OTFTs.
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http://dx.doi.org/10.1021/am101135vDOI Listing
February 2011

Enhanced charge transport in polymer thin-film transistors prepared by contact film transfer method.

ACS Appl Mater Interfaces 2009 Nov;1(11):2660-6

Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

The charge-carrier transport in the structures formed at the surface of various conjugated polymer films is investigated by constructing organic thin-film transistors using a novel and simple contact film transfer method. Thin-film transistors prepared by this transfer process have higher field-effect mobility values compared with conventional spin-coated devices for all the studied polymers. In contrast to previous reports, the hole mobility in regioregular poly(3-alkylthiophene)s does not depend on the length of the alkyl chain when the contact film transfer method is used. These results suggest that the thiophene rings adopt a highly ordered edge-on orientation and strong interchain pi-pi interactions spontaneously form at the polymer/air interface during the spin coating.
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http://dx.doi.org/10.1021/am9005572DOI Listing
November 2009

Bilayer ambipolar organic thin-film transistors and inverters prepared by the contact-film-transfer method.

ACS Appl Mater Interfaces 2009 Sep;1(9):1865-8

Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

Ambipolar organic thin-film transistors with a bilayer structure of poly(3-hexylthiophene) and [6,6]phenyl C(61) butyric acid methyl ester were fabricated using a simple solution-based, contact-film-transfer method. The transistors exhibited balanced electron and hole mobilities of 2.1 x 10(-2) and 1.1 x 10(-2) cm(2) V(-1) s(-1), respectively. Complementary inverters based on two identical ambipolar transistors showed good performance with a gain of 14.
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http://dx.doi.org/10.1021/am9004545DOI Listing
September 2009

Surface-segregated monolayers: a new type of ordered monolayer for surface modification of organic semiconductors.

J Am Chem Soc 2009 Dec;131(48):17597-604

Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

We report a new type of ordered monolayer for the surface modification of organic semiconductors. Fullerene derivatives with fluorocarbon chains ([6,6]-phenyl-C(61)-buryric acid 1H,1H-perfluoro-1-alkyl ester or FC(n)) spontaneously segregated as a monolayer on the surface of a [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) film during a spin-coating process from the mixture solutions, as confirmed by X-ray photoelectron spectroscopy (XPS). Ultraviolet photoelectron spectroscopy (UPS) showed the shift of ionization potentials (IPs) depending on the fluorocarbon chain length, indicating the formation of surface dipole moments. Surface-sensitive vibrational spectroscopy, sum frequency generation (SFG) revealed the ordered molecular orientations of the C(60) moiety in the surface FC(n) layers. The intensity of the SFG signals from FC(n) on the surface showed a clear odd-even effect when the length of the fluorocarbon chain was changed. This new concept of the surface-segregated monolayer provides a facile and versatile approach to modifying the surface of organic semiconductors and is applicable to various organic optoelectronic devices.
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http://dx.doi.org/10.1021/ja9057053DOI Listing
December 2009