Publications by authors named "Seyoung Kee"

13 Publications

  • Page 1 of 1

Halide Perovskites: Thermal Transport and Prospects for Thermoelectricity.

Adv Sci (Weinh) 2020 May 16;7(10):1903389. Epub 2020 Apr 16.

KAUST Solar Center Physical Science and Engineering Division King Abdullah University of Science and Technology Thuwal 23955-6900 Saudi Arabia.

The recent re-emergence of halide perovskites has received escalating interest for optoelectronic applications. In addition to photovoltaics, the multifunctional nature of halide perovskites has led to diverse applications. The ultralow thermal conductivity coupled with decent mobility and charge carrier tunability led to the prediction of halide perovskites as a possible contender for future thermoelectrics. Herein, recent advances in thermal transport of halide perovskites and their potentials and challenges for thermoelectrics are reviewed. An overview of the phonon behavior in halide perovskites, as well as the compositional dependency is analyzed. Understanding thermal transport and knowing the thermal conductivity value is crucial for creating effective heat dissipation schemes and determining other thermal-related properties like thermo-optic coefficients, hot-carrier cooling, and thermoelectric efficiency. Recent works on halide perovskite-based thermoelectrics together with theoretical predictions for their future viability are highlighted. Also, progress on modulating halide perovskite-based thermoelectric properties using light and chemical doping is discussed. Finally, strategies to overcome the limiting factors in halide perovskite thermoelectrics and their prospects are emphasized.
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http://dx.doi.org/10.1002/advs.201903389DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7237854PMC
May 2020

Elastic conducting polymer composites in thermoelectric modules.

Nat Commun 2020 Mar 18;11(1):1424. Epub 2020 Mar 18.

Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, 601 74, Norrköping, Sweden.

The rapid growth of wearables has created a demand for lightweight, elastic and conformal energy harvesting and storage devices. The conducting polymer poly(3,4-ethylenedioxythiophene) has shown great promise for thermoelectric generators, however, the thick layers of pristine poly(3,4-ethylenedioxythiophene) required for effective energy harvesting are too hard and brittle for seamless integration into wearables. Poly(3,4-ethylenedioxythiophene)-elastomer composites have been developed to improve its mechanical properties, although so far without simultaneously achieving softness, high electrical conductivity, and stretchability. Here we report an aqueously processed poly(3,4-ethylenedioxythiophene)-polyurethane-ionic liquid composite, which combines high conductivity (>140 S cm) with superior stretchability (>600%), elasticity, and low Young's modulus (<7 MPa). The outstanding performance of this organic nanocomposite is the result of favorable percolation networks on the nano- and micro-scale and the plasticizing effect of the ionic liquid. The elastic thermoelectric material is implemented in the first reported intrinsically stretchable organic thermoelectric module.
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http://dx.doi.org/10.1038/s41467-020-15135-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7080746PMC
March 2020

Enabling Free-Standing 3D Hydrogel Microstructures with Microreactive Inkjet Printing.

ACS Appl Mater Interfaces 2020 Jan 24;12(1):1832-1839. Epub 2019 Dec 24.

Reactive inkjet printing holds great prospect as a multimaterial fabrication process because of its unique advantages involving customization, miniaturization, and precise control of droplets for patterning. For inkjet printing of hydrogel structures, a hydrogel precursor (or cross-linker) is printed onto a cross-linker (or precursor) bath or a substrate. However, the progress of patterning and design of intricate hydrogel structures using the inkjet printing technique is limited by the erratic interplay between gelation and motion control. Accordingly, microreactive inkjet printing (MRIJP) was applied to demonstrate a spontaneous 3D printing of hydrogel microstructures by using alginate as the model system. In addition, a printable window within the capillary number-Weber number for the MRIJP technique demonstrated the importance of velocity to realization of in-air binary droplet collision. Finally, systematic analysis shows that the structure and diffusion coefficient of hydrogels are important factors that affect the shape of printed hydrogels over time. Based on such a fundamental understanding of MRIJP of hydrogels, the fabrication process and the structure of hydrogels can be controlled and adapt for 2D/3D microstructure printing of any low-viscosity (<40 cP) reactive inks, with a representative tissue-mimicking structure of a ∼200 μm diameter hollow tube presented in this work.
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http://dx.doi.org/10.1021/acsami.9b17192DOI Listing
January 2020

Direct Patterning of Highly Conductive PEDOT:PSS/Ionic Liquid Hydrogel via Microreactive Inkjet Printing.

ACS Appl Mater Interfaces 2019 Oct 27;11(40):37069-37076. Epub 2019 Sep 27.

Department of Mechanical Engineering , The University of Auckland , Symonds Street , Auckland 1010 , New Zealand.

The gelation of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has gained popularity for its potential applications in three dimensions, while possessing tissue-like mechanical properties, high conductivity, and biocompatibility. However, the fabrication of arbitrary structures, especially via inkjet printing, is challenging because of the inherent gel formation. Here, microreactive inkjet printing (MRIJP) is utilized to pattern various 2D and 3D structures of PEDOT:PSS/IL hydrogel by in-air coalescence of PEDOT:PSS and ionic liquid (IL). By controlling the in-air position and Marangoni-driven encapsulation, single droplets of the PEDOT:PSS/IL hydrogel as small as a diameter of ≈260 μm are fabricated within ≈600 μs. Notably, this MRIJP-based PEDOT:PSS/IL has potential for freeform patterning while maintaining identical performance to those fabricated by the conventional spin-coating method. Through controlled deposition achieved via MRIJP, PEDOT:PSS/IL can be transformed into different 3D structures without the need for molding, potentially leading to substantial progress in next-generation bioelectronics devices.
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http://dx.doi.org/10.1021/acsami.9b12069DOI Listing
October 2019

High-efficiency large-area perovskite photovoltaic modules achieved via electrochemically assembled metal-filamentary nanoelectrodes.

Sci Adv 2018 08 17;4(8):eaat3604. Epub 2018 Aug 17.

School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea.

Realizing industrial-scale, large-area photovoltaic modules without any considerable performance losses compared with the performance of laboratory-scale, small-area perovskite solar cells (PSCs) has been a challenge for practical applications of PSCs. Highly sophisticated patterning processes for achieving series connections, typically fabricated using printing or laser-scribing techniques, cause unexpected efficiency drops and require complicated manufacturing processes. We successfully fabricated high-efficiency, large-area PSC modules using a new electrochemical patterning process. The intrinsic ion-conducting features of perovskites enabled us to create metal-filamentary nanoelectrodes to facilitate the monolithic serial interconnections of PSC modules. By fabricating planar-type PSC modules through low-temperature annealing and all-solution processing, we demonstrated a notably high module efficiency of 14.0% for a total area of 9.06 cm with a high geometric fill factor of 94.1%.
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http://dx.doi.org/10.1126/sciadv.aat3604DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6097812PMC
August 2018

Highly Deformable and See-Through Polymer Light-Emitting Diodes with All-Conducting-Polymer Electrodes.

Adv Mater 2018 Jan 6;30(3). Epub 2017 Dec 6.

Department of Nanobio Materials and Electronics, School of Materials Science and Engineering, Heeger Center for Advanced Materials, Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju, 61005, Republic of Korea.

Despite the high expectation of deformable and see-through displays for future ubiquitous society, current light-emitting diodes (LEDs) fail to meet the desired mechanical and optical properties, mainly because of the fragile transparent conducting oxides and opaque metal electrodes. Here, by introducing a highly conductive nanofibrillated conducting polymer (CP) as both deformable transparent anode and cathode, ultraflexible and see-through polymer LEDs (PLEDs) are demonstrated. The CP-based PLEDs exhibit outstanding dual-side light-outcoupling performance with a high optical transmittance of 75% at a wavelength of 550 nm and with an excellent mechanical durability of 9% bending strain. Moreover, the CP-based PLEDs fabricated on 4 µm thick plastic foils with all-solution processing have extremely deformable and foldable light-emitting functionality. This approach is expected to open a new avenue for developing wearable and attachable transparent displays.
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http://dx.doi.org/10.1002/adma.201703437DOI Listing
January 2018

Highly Stretchable and Highly Conductive PEDOT:PSS/Ionic Liquid Composite Transparent Electrodes for Solution-Processed Stretchable Electronics.

ACS Appl Mater Interfaces 2017 Jan 27;9(1):819-826. Epub 2016 Dec 27.

School of Materials Science and Engineering and Department of Nanobio Materials and Electronics, and ‡Heeger Center for Advanced Materials and Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology , 123 Cheomdamgwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea.

Stretchable conductive materials have received great attention owing to their potential for realizing next-generation stretchable electronics. However, the simultaneous achievement of excellent mechanical stretchability and high electrical conductivity as well as cost-effective fabrication has been a significant challenge. Here, we report a highly stretchable and highly conducting polymer that was obtained by incorporating an ionic liquid. When 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) was added to an aqueous conducting polymer solution of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), it was found that EMIM TCB acts not only as a secondary dopant but also as a plasticizer for PEDOT:PSS, resulting in a high conductivity of >1000 S cm with stable performance at tensile strains up to 50% and even up to 180% in combination with the prestrained substrate technique. Consequently, by exploiting the additional benefits of high transparency and solution-processability of PEDOT:PSS, we were able to fabricate a highly stretchable, semitransparent, and wholly solution-processed alternating current electroluminescent device with unimpaired performance at 50% strain by using PEDOT:PSS/EMIM TCB composite films as both bottom and top electrodes.
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http://dx.doi.org/10.1021/acsami.6b11988DOI Listing
January 2017

Controlling Molecular Ordering in Aqueous Conducting Polymers Using Ionic Liquids.

Adv Mater 2016 Oct 8;28(39):8625-8631. Epub 2016 Aug 8.

School of Materials Science and Engineering and Department of Nanobio Materials and Electronics, Heeger Center for Advanced Materials and Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju, 500-712, Republic of Korea.

The molecular ordering of aqueous conducting polymers is controlled using a rational method. By introducing various ionic liquids, which have designed electrostatic interactions to PEDOT:PSS solutions, the evolution of the molecular ordering of the PEDOT is manipulated. Consequently, highly ordered nanostructures are achieved with a reduced π-π stacking distance of ≈3.38 Å and, thus, a maximum σ of ≈2100 S cm .
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http://dx.doi.org/10.1002/adma.201505473DOI Listing
October 2016

Long-Term Stable Recombination Layer for Tandem Polymer Solar Cells Using Self-Doped Conducting Polymers.

ACS Appl Mater Interfaces 2016 Mar 1;8(9):6144-51. Epub 2016 Mar 1.

Department of Nanobio Materials and Electronics (DNE), School of Materials Science and Engineering (SMSE) and ‡Research Institute for Solar and Sustainable Energies (RISE), Gwangju Institute of Science and Technology (GIST) , Gwangju 500-712, Korea.

Unlabelled: Recently, the most efficient tandem polymer solar cells (PSCs) have used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (

Pedot: PSS) as a p-type component of recombination layer (RL). However, its undesirable acidic nature, originating from insulating PSS, of

Pedot: PSS drastically reduces the lifetime of PSCs. Here, we demonstrate the efficient and stable tandem PSCs by introducing acid-free self-doped conducting polymer (SCP), combined with zinc oxide nanoparticles (ZnO NPs), as RL for

Pedot: PSS-free tandem PSCs. Moreover, we introduce an innovative and versatile nanocomposite system containing photoactive and p-type conjugated polyelectrolyte (p-CPE) into the tandem fabrication of an ideal self-organized recombination layer. In our new RL, highly conductive SCP facilitates charge transport and recombination process, and p-CPE helps to achieve nearly loss-free charge collection by increasing effective work function of indium tin oxide (ITO) and SCP. Because of the synergistic effect of extremely low electrical resistance, ohmic contact, and pH neutrality, tandem devices with our novel RL performed well, exhibiting a high power conversion efficiency of 10.2% and a prolonged lifetime. These findings provide a new insight for strategic design of RLs using SCPs to achieve efficient and stable tandem PSCs and enable us to review and extend the usefulness of SCPs in various electronics research fields.
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http://dx.doi.org/10.1021/acsami.5b11742DOI Listing
March 2016

Highly conductive all-plastic electrodes fabricated using a novel chemically controlled transfer-printing method.

Adv Mater 2015 Apr 23;27(14):2317-23. Epub 2015 Feb 23.

School of Materials Science and Engineering, Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology, Gwangju, 500-712, Republic of Korea.

A novel transfer-printing method for high-performance all-plastic transparent electrodes is demonstrated. A solution process using H2 SO4 not only dramatically enhances the electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) over 4000 S cm(-1) but also chemically modifies its adhesion properties, thereby enabling expeditious "pick-and-place" transfer onto arbitrary surfaces using elastomeric stamps. Flexible and transparent optoelectronic devices with transferred PEDOT:PSS electrodes show superb performances.
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http://dx.doi.org/10.1002/adma.201500078DOI Listing
April 2015

Simplified tandem polymer solar cells with an ideal self-organized recombination layer.

Adv Mater 2015 Feb 2;27(8):1408-13. Epub 2014 Dec 2.

School of Materials Science and Engineering, Department of Nanobio Materials and Electronics, Heeger Center for Advanced Materials, Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju, 500-712, South Korea.

A new tandem architecture for printable photovoltaics using a versatile organic nanocomposite containing photoactive and interfacial materials is demonstrated. The nanocomposite forms an ideal self-organized recombination layer via a spontaneous vertical phase separation, which yields a simplified tandem structure fabricated with only four component layers and a high tandem efficiency of 10.8%.
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http://dx.doi.org/10.1002/adma.201404765DOI Listing
February 2015

Highly conductive PEDOT:PSS nanofibrils induced by solution-processed crystallization.

Adv Mater 2014 Apr 16;26(14):2268-72, 2109. Epub 2013 Dec 16.

School of Materials Science and Engineering, Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology, Gwangju, 500-712, Republic of Korea.

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http://dx.doi.org/10.1002/adma.201304611DOI Listing
April 2014

Self-assembly of interfacial and photoactive layers via one-step solution processing for efficient inverted organic solar cells.

Nanoscale 2013 Dec 11;5(23):11587-91. Epub 2013 Oct 11.

School of Materials Science and Engineering, Department of Nanobio Materials and Electronics, Heeger Center for Advanced Materials, Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea.

Vertically self-assembled bilayers with an interfacial bottom layer and a photoactive top layer are demonstrated via a single coating step of a blend composed of an amine-containing nonconjugated polyelectrolyte (NPE) and an organic electron donor-acceptor bulk heterojunction composite. The self-assembled NPE layer reduces the work function of an indium tin oxide (ITO) cathode, which leads to efficient inverted organic solar cells without any additional interface engineering of the ITO.
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http://dx.doi.org/10.1039/c3nr04381aDOI Listing
December 2013