Jun-Chan Choi

Hoon Yeub Jeong

Dongwon Lee

Jonghyun Jeong

Junho Bae

Seongkwon Hwang

Junghwan Byun

Kyungjune Cho

Byeongmoon Lee

Seunghyun Lee

Hyunjoo Cho

Hyunjin Lee

Inho Jeong

FLEXLab, situated within the School of Electrical Engineering at Korea University, focuses on the advancement of flexible electronics. Its research encompasses the development of energy harvesting and storage devices, leveraging additive manufacturing techniques.

고려대학교 전기공학부의 FLEXLab은 첨단 플렉서블 전자 장치 개발에 주력한다. 에너지 수확 및 저장 장치 개발을 위해 적층 제조 기술을 활용하는 연구를 수행한다.

Charged-impurity free printing-based diffusion doping in molybdenum disulfide field-effect transistors

Auxetic mechanical metamaterials: efficient strain engineering for highly reliable free-form displays

Crosslinking site sharing-driven interface engineering to enhance adhesion between PDMS substrates and Ag–PDMS conductors

Enhanced Thermoelectric Performance of Carbon Nanotubes via Inkjet Printing-Based Surface Charge Transfer Doping

Mechanical metamaterial-based strain-programmable elastomer substrate for image-distortion-free stretchable displays

Recent progress in inkjet‐printed thin‐film transistors

High-performance compliant thermoelectric generators with magnetically self-assembled soft heat conductors for self-powered wearable electronics

Electronic skins for soft, compact, reversible assembly of wirelessly activated fully soft robots

All-inkjet-printed organic thin-film transistor inverter on flexible plastic substrate

Spin-coated Ga-doped ZnO transparent conducting thin films for organic light-emitting diodes

Direct patterning of colloidal quantum dots with adaptable dual-ligand surface

Substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes

Inkjet-printed stretchable silver electrode on wave structured elastomeric substrate

P-type CuO and Cu2O transistors derived from a sol–gel copper (II) acetate monohydrate precursor

Transparent Large-Area MoS 2 Phototransistors with Inkjet-Printed Components on Flexible Platforms

Recent advances in interface engineering of transition-metal dichalcogenides with organic molecules and polymers

Omnidirectional printing of elastic conductors for three-dimensional stretchable electronics

Enhanced charge injection properties of organic field‐effect transistor by molecular implantation doping

Lateral-crack-free, buckled, inkjet-printed silver electrodes on highly pre-stretched elastomeric substrates

Electrical Properties of Synthesized Large-Area MoS 2 Field-Effect Transistors Fabricated with Inkjet-Printed Contacts

Inkjet-printed stretchable single-walled carbon nanotube electrodes with excellent mechanical properties

Contact‐Engineered Electrical Properties of MoS 2 Field‐Effect Transistors via Selectively Deposited Thiol‐Molecules

A robust, gravure-printed, silver nanowire/metal oxide hybrid electrode for high-throughput patterned transparent conductors

Flexible high‐performance all‐inkjet‐printed inverters: organo‐compatible and stable interface engineering

Trap-mediated electronic transport properties of gate-tunable pentacene/MoS 2 p-n heterojunction diodes

Yongtaek Hong

TAKHEE LEE

Changhee Lee

Vivek Subramanian

Ali Javey

Jaewon Jang

Hoichang Yang

William Scheideler

Seungjun Chung

Drop‐on‐demand inkjet printing is one of the most attractive techniques from a manufacturing perspective due to the possibility of fabrication from a digital layout at ambient conditions, thus leading to great opportunities for the realization of low‐cost and flexible thin‐film devices. Over the past decades, a variety of inkjet‐printed applications including thin‐film transistors (TFTs), radio‐frequency identification devices, sensors, and displays have been explored. In particular, many research groups have made great efforts to realize high‐performance TFTs, for application as potential driving components of ubiquitous wearable electronics. Although there are still challenges to enable the commercialization of printed TFTs beyond laboratory‐scale applications, the field of printed TFTs still attracts significant attention, with remarkable developments in soluble materials and printing methodology. Here, recent progress in …

Softening of thermoelectric generators facilitates conformal contact with arbitrary-shaped heat sources, which offers an opportunity to realize self-powered wearable applications. However, existing wearable thermoelectric devices inevitably exhibit reduced thermoelectric conversion efficiency due to the parasitic heat loss in high-thermal-impedance polymer substrates and poor thermal contact arising from rigid interconnects. Here, we propose compliant thermoelectric generators with intrinsically stretchable interconnects and soft heat conductors that achieve high thermoelectric performance and unprecedented conformability simultaneously. The silver-nanowire-based soft electrodes interconnect bismuth-telluride-based thermoelectric legs, effectively absorbing strain energy, which allows our thermoelectric generators to conform perfectly to curved surfaces. Metal particles magnetically self-assembled in …

Designing softness into robots holds great potential for augmenting robotic compliance in dynamic, unstructured environments. However, despite the body’s softness, existing models mostly carry inherent hardness in their driving parts, such as pressure-regulating components and rigid circuit boards. This compliance gap can frequently interfere with the robot motion and makes soft robotic design dependent on rigid assembly of each robot component. We present a skin-like electronic system that enables a class of wirelessly activated fully soft robots whose driving part can be softly, compactly, and reversibly assembled. The proposed system consists of two-part electronic skins (e-skins) that are designed to perform wireless communication of the robot control signal, namely, “wireless inter-skin communication,” for untethered, reversible assembly of driving capability. The physical design of each e-skin features …

We report an all-inkjet-printed inverter using two p-type organic thin-film transistors (OTFTs) on a flexible plastic substrate. Metal-organic precursor-type silver ink, poly-4-vinylphenol solution, and 6,13-bis (triisopropylsilylethynyl)-pentacene solution were used to print gate and source/drain electrodes, gate-dielectric layer, and active semiconductor layer, respectively. By optimizing fabrication conditions, we obtained OTFTs with a mobility of 0.02 cm 2 /V·s, an on/off ratio of 10 4 , and a threshold voltage of -1.2 V, and inverters with good switching performance showing a gain of 7.8 at a supply voltage of V DD = -40 V .

Gallium doped zinc oxide (GZO) thin films have been prepared by a simple sol–gel spin coating technique. XRD results showed the preferential c -axis orientation of the crystallites and the presence of the wurtzite phase of ZnO. A lowest resistivity of 3.3 × 10 −3 Ω cm was obtained for the ZnO film doped with 2 at% of Ga after post-annealing at 500 °C for 45 min in a H 2 atmosphere. All the films showed more than 80% of transparency in the entire visible region. Blue shifting of the optical band gap was observed with an increase in Ga doping, which can be explained on the basis of the Burstein–Moss effect. OLED devices were fabricated using 2 at% Ga-doped ZnO thin films as anodes. Preliminary results obtained demonstrated that spin-coated GZO films can be used as a promising TCO for optoelectronic device applications.

Colloidal quantum dots (QDs) stand at the forefront of a variety of photonic applications given their narrow spectral bandwidth and near-unity luminescence efficiency. However, integrating luminescent QD films into photonic devices without compromising their optical or transport characteristics remains challenging. Here we devise a dual-ligand passivation system comprising photocrosslinkable ligands and dispersing ligands to enable QDs to be universally compatible with solution-based patterning techniques. The successful control over the structure of both ligands allows the direct patterning of dual-ligand QDs on various substrates using commercialized photolithography (i-line) or inkjet printing systems at a resolution up to 15,000 pixels per inch without compromising the optical properties of the QDs or the optoelectronic performance of the device. We demonstrate the capabilities of our approach for QD-LED …

We report substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes (OLEDs). Heat dissipation behavior of top-emission OLEDs fabricated on silicon, glass, and planarized stainless steel substrates was measured by using an infrared camera. Peak temperature measured from the backside of each substrate was saturated to be 21.4, 64.5, and 40.5 C⁠, 180 s after the OLED was operated at luminance of 10 000 cd/m 2 and 80% luminance lifetime was about 198, 31, and 96 h, respectively. Efficient heat dissipation through the highly thermally conductive substrates reduced temperature increase, resulting in much improved OLED lifetime.

We report high performance and stable inkjet-printed stretchable silver electrodes on wave structured elastomeric substrates. Highly conductive silver electrodes were deposited directly on a ultraviolet ozone treated polydimethylsiloxane (PDMS) substrates having vertical wavy structures. Adhesion between printed silver lines and PDMS surface has been enhanced by intentionally roughened PDMS surface with wire-electro discharge machined aluminum mold. During slow (16.7 μ m/s) stretching test, resistance of the printed silver electrode was increased only by three times at 30% tensile strain. Inkjet-printed silver electrodes also showed good mechanical stability during 1000-time fast (1 mm/s) cycling test with 10% tensile strain, showing maximum resistance change of less than three times.

We realize p-type thin film transistors (TFT) with solution-processed channels using a sol–gel route, based on a copper (II) acetate precursor. The sol–gel process initially produces Cu, which is then oxidized depending on sintering conditions to produce Cu 2 O and ultimately CuO. These processes are performed at temperatures no higher than 500 °C, and are therefore compatible with standard display glass substrates for use in transparent display applications. To control the film morphology of the sol–gel processed copper oxide layer, additional water was added to the precursor solution. As the water to alkoxide ratio is increased, the degree of hydrolysis increased, thus increasing the grain size of CuO and Cu 2 O. The resulting p-type CuO and Cu 2 O TFTs exhibited improved thin film transistor performance, including field effect mobilities of 1.0 × 10 − 2 cm 2 /Vs and 2.0 × 10 − 3 cm 2 /Vs, respectively, and an on/off …

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have gained considerable attention as an emerging semiconductor due to their promising atomically thin film characteristics with good field-effect mobility and a tunable band gap energy. However, their electronic applications have been generally realized with conventional inorganic electrodes and dielectrics implemented using conventional photolithography or transferring processes that are not compatible with large-area and flexible device applications. To facilitate the advantages of 2D TMDCs in practical applications, strategies for realizing flexible and transparent 2D electronics using low-temperature, large-area, and low-cost processes should be developed. Motivated by this challenge, we report fully printed transparent chemical vapor deposition (CVD)-synthesized monolayer molybdenum disulfide (MoS 2 ) phototransistor arrays on flexible …

The interface engineering of two-dimensional (2D) transition-metal dichalcogenides (TMDs) has been regarded as a promising strategy to modulate their outstanding electrical and optoelectronic properties because of their inherent 2D nature and large surface-to-volume ratio. In particular, introducing organic molecules and polymers directly onto the surface of TMDs has been explored to passivate the surface defects or achieve better interfacial properties with neighboring surfaces efficiently, thus leading to great opportunities for the realization of high-performance TMD-based applications. This review provides recent progress in the interface engineering of TMDs with organic molecules and polymers corresponding to the modulation of their electrical and optoelectronic characteristics. Depending on the interfaces between the surface of TMDs and dielectric, conductive contacts or the ambient environment, we …

Three-dimensional printing could be used to create complex and multifunctional soft electronic devices. However, printing solid-state elastic conductors with three-dimensional geometries is challenging because the rheological properties of existing inks typically only allow for layer-wise deposition. Here we show that an emulsion system—consisting of a conductive elastomer composite, immiscible solvent and emulsifying solvent—can be used for the omnidirectional printing of elastic conductors. The viscoelastic properties of the composite provide structural integrity to the printed features—allowing freestanding, filamentary and out-of-plane three-dimensional geometries to be directly written—and pseudo-plastic and lubrication behaviours that provide printing stability and prevent nozzle clogging. Printed structures of the intrinsically stretchable conductor exhibit a minimum feature size less than 100 μm and …

Organic semiconductors (OSCs) have been widely studied due to their merits such as mechanical flexibility, solution processability, and large‐area fabrication. However, OSC devices still have to overcome contact resistance issues for better performances. Because of the Schottky contact at the metal–OSC interfaces, a non‐ideal transfer curve feature often appears in the low‐drain voltage region. To improve the contact properties of OSCs, there have been several methods reported, including interface treatment by self‐assembled monolayers and introducing charge injection layers. Here, a selective contact doping of 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F 4 ‐TCNQ) by solid‐state diffusion in poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) to enhance carrier injection in bottom‐gate PBTTT organic field‐effect transistors (OFETs) is demonstrated. Furthermore, the effect of …

We report the formation of lateral-crack-free silver electrodes on highly pre-stretched poly(dimethylsiloxane) (PDMS) substrates using the inkjet-printing method followed by an annealing process under the pre-stretched state. Due to Poisson's effect, cracks are easily obtained in the direction lateral to the pre-stretching and releasing directions when the highly pre-stretched substrate is released after the electrode formation. In our method, however, Poisson's effect is suppressed significantly from the PDMS thermal expansion perpendicular to the pre-stretched direction during the annealing process. In order to prevent the formation of a lateral crack, the annealing temperature needs to be optimized for each pre-stretching condition. We modelled their relationship using Poisson's ratios and thermal expansion coefficients of the substrate and silver materials. Our measurement results showed consistent result with the …

We report the electrical properties of synthesized large-area monolayer molybdenum disulfide (MoS 2 ) field-effect transistors (FETs) with low-cost inkjet-printed Ag electrodes. The monolayer MoS 2 film was grown by a chemical vapor deposition (CVD) method, and the top-contact Ag source/drain electrodes (S/D) were deposited onto the films using a low-cost drop-on-demand inkjet-printing process without any masks and surface treatments. The electrical characteristics of FETs were comparable to those fabricated by conventional deposition methods such as photo- or electron beam lithography. The contact properties between the S/D and the semiconductor layer were also evaluated using the Y-function method and an analysis of the output characteristic at the low drain voltage regimes. Furthermore, the electrical instability under positive gate-bias stress was studied to investigate the charge-trapping mechanism …

Inkjet-printed single-walled carbon nanotube (SWCNT) thin films on stretchable substrates were developed, and their electrical properties were investigated. The 1-and 5-layer printed SWCNT thin films had sheet resistances of 169.76 and 19.08 Ω/sq, respectively, and maintained conductive properties under 100% tensile strain. A nitric acid treatment significantly improved the conductivity of the SWCNT electrodes, and after an initial increase, the 5-layer printed SWCNT electrodes showed a normalized resistance of less than 1.2 after 1000 cycles under 100% tensile strain. The potential of the inkjet-printed SWCNT thin films for stretchable electrode applications was demonstrated via integration with a light-emitting diode.

Although 2D molybdenum disulfide (MoS 2 ) has gained much attention due to its unique electrical and optical properties, the limited electrical contact to 2D semiconductors still impedes the realization of high‐performance 2D MoS 2 ‐based devices. In this regard, many studies have been conducted to improve the carrier‐injection properties by inserting functional paths, such as graphene or hexagonal boron nitride, between the electrodes and 2D semiconductors. The reported strategies, however, require relatively time‐consuming and low‐yield transfer processes on sub‐micrometer MoS 2 flakes. Here, a simple contact‐engineering method is suggested, introducing chemically adsorbed thiol‐molecules as thin tunneling barriers between the metal electrodes and MoS 2 channels. The selectively deposited thiol‐molecules via the vapor‐deposition process provide additional tunneling paths at the contact regions …

High-throughput patterning and enhanced mechanical stability are key to enabling large-area applications of metal nanowire mesh transparent electrodes. In this work, hybrid transparent conductors based on silver nanowires embedded in an indium zinc oxide matrix were prepared by high-speed gravure-printing (1.0 m s−1) from a single, stable liquid precursor. These gravure-printed films demonstrate excellent conductivity (9.3 Ω □−1) and transparency (T550nm ∼ 91%), as well as robust mechanical properties. The encapsulating indium zinc oxide matrix dramatically improves adhesion, surface roughness (Rq < 5 nm), film uniformity, and thermal stability (up to 350 °C) of the embedded silver nanowires. These properties of the hybrid films make them a suitable electrode material for a variety of printed electronic devices, such as flexible OLEDs and solar cells.

Vacuum-or solution-processed organic thin-film transistors (OTFTs) have shown high electrical performance equal or superior to that achieved by amorphous silicon-based devices, which are difficult to manipulate on plastic substrates owing to their high processing temperature.[1–6] Recently, solution-printed OTFTs have been reported as potential driving components for flexible and large-area electronics applications.[7–9] Among large-scale solution printing methods, maskless and noncontact inkjet-printing is one of the most promising methods for fabricating all-solution-processed OTFTs.[10, 11] However, only a few groups have reported all-inkjet-printed OTFTs [12, 13] and circuits,[14, 15] due to the difficulties in optimizing inkjet-printing and other post-treatments, specifically, organo-compatible, stable interfaces of organic semiconductors at both printed metal electrodes and gate dielectrics. Moreover, owing to …

We investigated the trap-mediated electronic transport properties of pentacene/molybdenum disulphide (MoS 2 ) p-n heterojunction devices. We observed that the hybrid p-n heterojunctions were gate-tunable and were strongly affected by trap-assisted tunnelling through the van der Waals gap at the heterojunction interfaces between MoS 2 and pentacene. The pentacene/MoS 2 p-n heterojunction diodes had gate-tunable high ideality factor, which resulted from trap-mediated conduction nature of devices. From the temperature-variable current-voltage measurement, a space-charge-limited conduction and a variable range hopping conduction at a low temperature were suggested as the gate-tunable charge transport characteristics of these hybrid p-n heterojunctions. Our study provides a better understanding of the trap-mediated electronic transport properties in organic/2-dimensional material hybrid heterojunction …

FLEX Laboratory

교수님 소개

정승준

연구실 소개

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Auxetic mechanical metamaterials: efficient strain engineering for highly reliable free-form displays

Crosslinking site sharing-driven interface engineering to enhance adhesion between PDMS substrates and Ag–PDMS conductors

Enhanced Thermoelectric Performance of Carbon Nanotubes via Inkjet Printing-Based Surface Charge Transfer Doping

연구실 보유 특허

대학별 입시끈

우리 연구실 모집

교수님 소개

정승준

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Auxetic mechanical metamaterials: efficient strain engineering for highly reliable free-form displays

Crosslinking site sharing-driven interface engineering to enhance adhesion between PDMS substrates and Ag–PDMS conductors

Enhanced Thermoelectric Performance of Carbon Nanotubes via Inkjet Printing-Based Surface Charge Transfer Doping

연구실 보유 특허

최근 3년간 연구실적 높은 연구실

대학별 입시끈

우리 연구실 모집