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Solution-Processable Conductive Graphene-Based Materials for Flexible Electronics
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis work explores electrical conductors based on few-layer graphene flakes as an enabler for low-cost, mechanically flexible, and high-conductivity conductors in large area flexible and printed electronic devices. The flakes are deposited from aqueous solutions and processed at low temperature.

Graphene is selected for its excellent properties in mechanical, optical, electronic, and electrical aspects. However, thin films of pristine few-layer graphene flakes deposited from dispersions normally exhibit inferior electrical conductivity. One cause responsible for this problem is the loose stacking and random orientation of graphene flakes in a graphene deposition. We have solved this problem by implementing a simple post-deposition treatment leading to dramatically densified and planarized thin films. Significantly increased electrical conductivity by ~20 times is obtained. The 1-pyrenebutyric acid tetrabutylammonium salt as an exfoliation enhancer and dispersant in water yields ~110 S/m in conductivity when the graphene based thin films are processed at 90 °C. In order to achieve higher conductivity, a room-temperature method for site-selective copper electroless deposition has been developed. This method is of particular interest for the self-aligned copper deposition to the predefined graphene films. The resultant two-layer graphene/copper structure is characterized by an overall conductivity of ~7.9 × 105 S/m, an increase by ~7000 times from the template graphene films. Several electronic circuits based on the graphene/copper bilayer interconnect have been subsequently fabricated on plastic foils as proof-of-concept demonstrators. Alternatively, highly conductive composites featuring graphene flakes coated with silver nanoparticles with electrical conductivity beyond 106 S/m can be readily obtained at 100 oC. Moreover, a highly conductive reduced-graphene-oxide/copper hybrid hydrogel has been achieved by mixing aqueous graphene oxide solution and copper-containing Fehling's solution. The corresponding aerogel of high porosity exhibits an apparent electrical conductivity of ~430 S/m and delivers a specific capacity of ~453 mAh g−1 at current density of 1 A/g. The experimental results presented in this thesis show that the solution-phase, low-temperature fabrication of highly conductive graphene-based materials holds promises for flexible electronics and energy storage applications. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 65
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1799
Keywords [en]
Graphene, Graphene oxide, Silver, Copper, Composite, Conductive inks, Flexible electronics, Printed electronics
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
URN: urn:nbn:se:uu:diva-381348ISBN: 978-91-513-0636-0 (print)OAI: oai:DiVA.org:uu-381348DiVA, id: diva2:1303078
Public defence
2019-06-12, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen. 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-05-13 Created: 2019-04-08 Last updated: 2019-06-18
List of papers
1. Re-organized graphene nanoplatelet thin films achieved by a two-step hydraulic method
Open this publication in new window or tab >>Re-organized graphene nanoplatelet thin films achieved by a two-step hydraulic method
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2018 (English)In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 84, p. 141-145Article in journal (Refereed) Published
Abstract [en]

Film deposition of graphene nanoplatelets (GNPs) from dispersion via casting and printing approaches features cost- and material-efficiency, however, it usually suffers from poor uniformity, rough surface and loose flake stacking due to adverse effect of hydraulic force. Here, a simple two-step method exploiting hydraulic force is presented to readily deliver GNP films of improved quality from an aqueous dispersion. While as-deposited GNP films exhibit the aforementioned film defects, the hydraulic force in the subsequent step constituting soaking in water and drying leads to an efficient re-organization of the individual GNPs in the films, The majority of GNPs thus are oriented horizontally and closely stacked. As a result, densified, smoothened and homogenized GNP thin films can be readily achieved. The GNP re-organization reduces resistivity from > 1 Omega cm to 10(-2) Omega cm. The method developed is universally applicable to solution-phase film deposition of 2D materials.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:uu:diva-356327 (URN)10.1016/j.diamond.2018.03.016 (DOI)000432101800019 ()
Funder
Swedish Foundation for Strategic Research , Dnr SE13-0061Swedish Research Council, 621-2014-5596
Available from: 2018-07-26 Created: 2018-07-26 Last updated: 2019-04-08Bibliographically approved
2. A Sequential Process of Graphene Exfoliation and Site-Selective Copper/Graphene Metallization Enabled by Multifunctional 1-Pyrenebutyric Acid Tetrabutylammonium Salt
Open this publication in new window or tab >>A Sequential Process of Graphene Exfoliation and Site-Selective Copper/Graphene Metallization Enabled by Multifunctional 1-Pyrenebutyric Acid Tetrabutylammonium Salt
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2019 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 6, p. 6448-6455Article in journal (Refereed) Published
Abstract [en]

This paper reports a procedure leading to shear exfoliation of pristine few-layer graphene flakes in water and subsequent site-selective formation of Cu/graphene films on polymer substrates, both of which are enabled by employing the water soluble 1-pyrenebutyric acid tetrabutylammonium salt (PyB-TBA). The exfoliation with PyB-TBA as an enhancer leads to as-deposited graphene films dried at 90 °C that are characterized by electrical conductivity of ∼110 S/m. Owing to the good affinity of the tetrabutylammonium cations to the catalyst PdCl42–, electroless copper deposition selectively in the graphene films is initiated, resulting in a self-aligned formation of highly conductive Cu/graphene films at room temperature. The excellent solution-phase and low-temperature processability, self-aligned copper growth, and high electrical conductivity of the Cu/graphene films have permitted fabrication of several electronic circuits on plastic foils, thereby indicating their great potential in compliant, flexible, and printed electronics.

Keywords
graphene, electroless copper deposition, solution-phase processing, self-aligned metallization, flexible electronics
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-378999 (URN)10.1021/acsami.8b21162 (DOI)000459221900096 ()30656938 (PubMedID)
Funder
Swedish Foundation for Strategic Research , Dnr SE13-0061Swedish Research Council, 621-2014-5596
Available from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-04-08Bibliographically approved
3. Microstructure-tunable highly conductive graphene-metal composites achieved by inkjet printing and low temperature annealing
Open this publication in new window or tab >>Microstructure-tunable highly conductive graphene-metal composites achieved by inkjet printing and low temperature annealing
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2018 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 28, no 3, article id 035006Article in journal (Refereed) Published
Abstract [en]

We present a method for fabricating highly conductive graphene-silver composite films with a tunable microstructure achieved by means of an inkjet printing process and low temperature annealing. This is implemented by starting from an aqueous ink formulation using a reactive silver solution mixed with graphene nanoplatelets (GNPs), followed by inkjet printing deposition and annealing at 100 degrees C for silver formation. Due to the hydrophilic surfaces and the aid of a polymer stabilizer in an aqueous solution, the GNPs are uniformly covered with a silver layer. Simply by adjusting the content of GNPs in the inks, highly conductive GNP/Ag composites (> 106 S m(-1)), with their microstructure changed from a large-area porous network to a compact film, is formed. In addition, the printed composite films show superior quality on a variety of unconventional substrates compared to its counterpart without GNPs. The availability of composite films paves the way to the metallization in different printed devices, e.g. interconnects in printed circuits and electrodes in energy storage devices.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
graphene, composite, inkjet printing
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-345709 (URN)10.1088/1361-6439/aaa450 (DOI)000423867400001 ()
Funder
Swedish Foundation for Strategic Research , Dnr SE13-0061Swedish Research Council, 621-2014-5596
Available from: 2018-03-14 Created: 2018-03-14 Last updated: 2019-04-08Bibliographically approved
4. High-Conductivity Reduced-Graphene-Oxide/Copper Aerogel for Energy Storage
Open this publication in new window or tab >>High-Conductivity Reduced-Graphene-Oxide/Copper Aerogel for Energy Storage
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2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 60, p. 760-767Article in journal (Refereed) Published
Abstract [en]

This work reports a room-temperature, solution-phase and one-pot method for macro-assembly of a three-dimensional (3D) reduced-graphene-oxide/copper hybrid hydrogel. The hydrogel is subsequently transformed into a highly conductive aerogel via freeze-drying. The aerogel, featuring reduced graphene oxide (rGO) networks decorated with Cu and CuxO nanoparticles (Cu/CuxO@rGO), exhibits a specific surface area of 48 m(2)/g and an apparent electrical conductivity of similar to 33 and similar to 430 S/m prior to and after mechanical compression, respectively. The compressed Cu/CuxO@rGO aerogel delivers a specific capacity of similar to 453 mAh g(-1) at a current density of 1 A/g and similar to 184 mAh g(-1) at 50 A/g in a 3 M KOH aqueous electrolyte evidenced by electrochemical measurements. Galvanostatic cycling tests at 5 A/g demonstrates that the Cu/CuxO@rGO aerogel retains 38% (similar to 129 mAh g(-1)) of the initial capacity (similar to 339 mAh g(-1)) after 500 cycles. The straightforward manufacturing process and the promising electrochemical performances make the Cu/CuxO@rGO aerogel an attractive electrode candidate in energy storage applications.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-381347 (URN)10.1016/j.nanoen.2019.04.023 (DOI)000467774100084 ()
Funder
Swedish Foundation for Strategic Research , Dnr SE13-0061Swedish Research Council, 621-2014-5596
Available from: 2019-04-08 Created: 2019-04-08 Last updated: 2019-06-11Bibliographically approved

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