Jae-Wook Kang

Chonbuk National University | cbnu · Department of Flexible and Printable Electronics

Fiber‐shaped energy storage devices have great potential for use as an intelligent power source for futuristic wearable technology. To produce high‐performance fiber‐shaped energy storage devices, a thin fiber material with a high energy density, shape adaptability, and longevity is critical. Herein, 3D fiber‐shaped supercapacitors (SCs) comprising...

Formamidinium lead bromide (FAPbBr3) nanocrystals (NCs) that exhibit ultra‐pure green emission are the most promising candidates for future displays. Despite the rapid development of light‐emitting diodes (LEDs) based on perovskite NCs (PeNCs), there is limited research detailing their intrinsic light outcoupling. Herein, the use of a short‐chain f...

The development of anti‐solvent free, scalable, and printable perovskite film is crucial to realizing the low‐cost roll‐to‐roll development of perovskite solar cells (PSCs). Herein, large‐area perovskite film fabrication is explored using a spray‐assisted sequential deposition technique. How propylene carbonate (PC) solvent additive affects the tra...

2D tin‐based perovskites have gained considerable attention for use in diverse optoelectronic applications, such as solar cells, lasers, and thin‐film transistors (TFTs), owing to their good stability and optoelectronic properties. However, their intrinsic charge‐transport properties are limited, and the insulating bulky organic ligands hinder the...

In recent years, researchers have developed spray deposition technology to fabricate tin oxide electron transport layer (ETL) with the aim of manufacturing high‐efficiency, large‐area perovskite solar cell (PSC). However, the power conversion efficiency (PCE) of PSC based on sprayed SnO 2 ETL remains inferior to that of the spin‐coated SnO 2 ETL. H...

Developing an efficient electron transport layer (ETL) through structural modification is essential to produce perovskite solar cells (PSCs) with high power conversion efficiency (PCE). Specifically, the ETL should exhibit low...

Solution‐processed formamidinium lead iodide (FAPbI3) perovskite typically contains a high number of ionic defects that are intrinsically formed during film formation. To reduce the defects, postsynthetic surface passivation treatment is widely practiced. However, the practicality of the surface passivation approach is limited by the poor coverage...

Solution‐processed formamidinium lead iodide (FAPbI3) perovskite is entropically metastable, and it exhibits condition‐induced crystal polymorphism. Under an ambient atmosphere, the photoactive black α‐FAPbI3 converts easily to photoinactive yellow δ‐FAPbI3. This α → δ phase degradation is further accelerated upon exposure to high temperature/humid...

Unprecedentedly, cesium lead halide (CsPbX 3 , X ¼ Cl, Br, I) quantum dots (QDs) with tunable spectral emissions and photophysical properties are used as a common emissive material for the fabrication of full-color perovskite QDs light-emitting diodes. An efficient, non-destructive ligand/anion exchange strategy is developed to fine-tune the optica...

Non‐toxic heavy metal, low‐cost indium‐free blue emissive quantum dots (QDs) are critical for the realization of self‐emissive electroluminescent quantum dot (ELQD) light‐emitting diode (LED) displays. A facile and effective hybridization of ZnO QDs with functionalized polyaromatic hydrocarbons (f‐PAHs) to synthesize a very bright and stable blue‐l...

We studied the effects that internal porous structures tailored using size-controlled copper nanosheets (Cu NSs) had on the electromagnetic interference (EMI) shielding performance of the resulting Cu NS films. Cu NSs were carefully synthesized as two-dimensional (2D) conductive fillers, and their size was controlled by adjusting the concentrations...

The photovoltaic performance and scalability potential of a semitransparent perovskite solar cells (ST-PSCs) are primarily determined by the optoelectronic properties of the top transparent conducting electrode (TCE) used. Herein, we demonstrate the scalable fabrication of ST-PSC using a three-dimensional (3D) TCE consisting of (i) a sputtered amor...

The performance and scalability of perovskite solar cells (PSCs) is highly dependent on the morphology and charge selectivity of the electron transport layer (ETL). This work demonstrates a high‐speed (1800 mm min⁻¹), room‐temperature (25 °C–30 °C) deposition of large‐area (62.5 cm²) tin oxide films using a multi‐pass spray deposition technique. Th...

Solution‐processed perovskite films are rich in surface defects and grain boundaries, which limits their performance and stability in photovoltaic application. Surface passivation using bulky organic cations can effectively reduce the surface defects of perovskite film without affecting its fundamental properties. In this work, we introduce the use...

Roll-to-roll (R2R) fabrication of flexible and transparent all-solid-state supercapacitors (FT-ASSCs) is extremely challenging because of the classic trade-off between transparency and capacitance. In this work, we develop fully three-dimensional (3D)-printed, sandwich-type FT-ASSCs comprised of 3D line-patterned carbon black (CB)/Ag/CB electrodes...

All inorganic CsPbBr3 perovskite quantum dots (PeQDs) have emerged as great candidates for next-generation perovskite light-emitting diodes (PeQLEDs) applications due to their excellent optoelectronic and light-emitting properties. However, the performance of CsPbBr3 based PeQLEDs is hindered by (i) the long-chain, synthetic insulating ligands on P...

Hybrid lead-halide perovskites are widely used in a variety of optoelectronic applications, including perovskite solar cells (PSCs), perovskite light-emitting diodes (PeLEDs), perovskite photodetectors (PPDs), and scintillators. Recently, it was demonstrated that bulky organic cations (BOCs) can be used as surface passivation agents to fine-tune th...

Flexible organic light emitting diodes (OLEDs) are used widely in optoelectronic devices, with possible new applications including foldable/rollable displays. Unique features of flexible OLEDs included high brightness, low power consumption and flexibility. The performance of a flexible OLED is frequently hindered by refractive index difference bet...

Fiber-shaped solar cells have attracted significant attention for their potential applications in portable and wearable electronics. Developing highly efficient and stable counter electrodes (CEs) to replace rare and expensive noble metals in dye-sensitized solar cells (DSSCs) is a research challenge. The low cost, excellent activity, and stability...

The popularity of wearable smart electronic gadgets, such as smartphones, smartwatches, and medical sensors, is inhibited by their limited operation lifetime due to the lack of a sustainable self‐charging power supply. This constraint can be overcome by developing a flexible, self‐charging photocapacitor that can synchronously harvest and store ene...

State‐of‐the‐art perovskite solar cells (PSCs) based on three‐dimensional (3D) films have achieved high power conversion efficiencies (PCEs), but are relatively fragile in high‐temperature and humid environments. This shortcoming must be addressed before PSCs can be fully commercialized. Herein, the use of a fluorinated aromatic organic spacer cati...

Organic light-emitting diodes (OLEDs) are widely commercialized in the display market due to many advantages such as wide color gamut, outstanding flexibility, and high contrast ratio. However, the performance of OLED is often hindered by the refractive index differences between the anode, substrate, and air, leading to inefficient light out-coupli...

Dye-sensitized solar cells (DSSCs) have attracted intense scientific interest due to their low cost, environmentally friendly operation, and relatively high efficiency. In particular, solid-state fiber dye-sensitized solar cells (SS-FDSSCs) have attracted significant attention for their potential applications in portable, flexible, and wearable ele...

State-of-the-art perovskite solar cells (PSCs) have achieved a record-breaking power conversion efficiency (PCE) of 25.2% with remarkable operational stability, surpassing the PCE of silicon-based solar cells. In the pristine state, bulk perovskite film often exhibits intrinsic interstitial/vacancies defects, and non-coordinated ions especially at...

We present the fabrication of flexible all-solid-state micro-supercapacitors (MSCs) by using 3D direct-ink-writing (DIW) technique. The conductive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) ink was printed by layer-by-layer fashion on flexible substrates. The MSC electrodes exhibit smooth surface and low sheet resistance. T...

We propose a new fabrication method of high thermally conductive epoxy composites for 3 D printing technology, which is based on a thermosetting epoxy system containing graphene nanoplate (GNP) as an IR-absorbing material. Firstly, we developed highly heat-dissipating inks based on bisphenol A diglycidyl ether (DGEBA) type epoxy resins containing g...

Recent studies are actively contributing to the implementation of the use of five human senses in electronic skins. In order to achieve this, it is critical to develop sensors with the ability to heal after being subjected to stretching or damage; this should be achieved without any significant deterioration in performance, as is possible for human...

Polyvinylidene fluoride (PVDF) has been applied in various industries due to its excellent piezoelectric property. In this study, the optimization of various processing conditions such as poling strength, poling duration and the surface morphology (angle) of the sensors were systematically investigated for large-area tactile sensor based on a 0.8 m...

We report a method of constructing an active optical polarizer by aligned carbon nanotube (CNT) sheet that is flexible, bendable, transparent, conductive, and also served to anchor liquid-crystal (LC) molecules. A horizontally-aligned CNT sheet was obtained by mechanical stretching from a vertically grown CNT forest, which was then transferred onto...

As demonstrated by Jin‐Woo Oh, Jae‐Wook Kang and co‐workers in article number 1902080, the M13 bacteriophage can be used as a biological scaffold for the controlled densification of silver and gold nanoparticles, yielding a novel biohybrid nanostructure with fascinating gap‐plasmon effect. The binder‐free, charge driven synthesis mechanism of the n...

In this work, we report large-area, semi-transparent, and flexible all-solid-state supercapacitors (ASSCs) fabricated using scalable D-bar coating, which is compatible with roll-to-roll printing processes. The poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS)-based transparent conducting electrodes (TCEs) show optical transpare...

Organic light emitting diodes (OLEDs), which possess wonderful device performance and mechanical robustness have been extensively explored in textile lighting applications. In this work, an ITO‐free, PEDOT:PSS/Ag‐fiber hybrid transparent conducting electrode (TCE) embedded in polymeric substrate (denoted as hybrid‐fiber TCE henceforth) for the fabr...

Improving the ohmic contact and interfacial morphology between an electron transport layer (ETL) and perovskite film is the key to boost the efficiency of planar perovskite solar cells (PSCs). In the current work, an amorphous–crystalline heterophase tin oxide bilayer (Bi‐SnO2) ETL is prepared via a low‐temperature solution process. Compared with t...

We determine the influence of substitutional defects on perovskite quantum dots through experimental and theoretical investigations. Substitutional defects were introduced by trivalent dopants (In, Sb, and Bi) in CsPbBr3 by ligand-assisted reprecipitation. We show that the photoluminescence (PL) emission peak shifts toward shorter wavelengths when...

Plasmonic nanostructures, which exhibit prominent localized surface plasmon resonance (LSPR) properties, are highly desirable for organic solar cells (OSC) and organic light‐emitting diode (OLED) devices. In the present work, novel plasmonic bio‐nanostructures are successfully synthesized via the self‐densification of silver (Ag) and gold (Au) meta...

Non-toxic, inexpensive, and eco-friendly fluorescent materials of colloidal oxide semiconductor quantum dots (QDs) are very promising In-free candidates for QD-based light emitting diodes (LEDs) to replace hazardous Cd- and Pb-based QDs. Super-Eg excitation wavelength (λex) dependent Zni-VO complex defects related characteristic emissions of green,...

Technological advancement in portable electronic devices is often inhibited by the inadequate capacity of energy-storage devices. Asymmetric all-solid-state supercapacitors (ASSCs) can overcome energy-storage limitations of symmetric ASSCs by utilizing two different electrodes to extend the operating voltage window without decomposition of the elec...

Fabrication of high-quality, low-cost and large-scale solution processable inorganic hole-transport layers (HTLs) for planar p-i-n perovskite solar cells (PSCs) is still a challenge that must be overcome to produce stable devices. Herein, we demonstrate the development of large-scale (>60 cm²), highly uniform and dopant-free NiO films via spray pyr...

Paper-based electronics is an emerging technology that is attracting attention for its high flexibility, ease of recycling/disposal, low manufacturing cost, and scalability. In this work, graphene flakes dispersion was coated on the mulberry papers through a simple Meyer-rod coating process. The characteristics of the mulberry paper-based graphene...

Hole transport materials (HTMs) with different hole extraction abilities play an important role in dictating the efficiency of the perovskite solar cells (PSCs). Besides, employing a donor acceptor (D-A) random copolymer HTM to bring out deeper HOMO energy level is highly beneficial to the hole extraction and durability of PSCs. In this context, a...

Solution‐processed triple‐cation perovskite solar cells (PSCs) rely on complex compositional engineering or delicate interfacial passivation to balance the trade‐off between cell efficiency and long‐term stability. Herein, the facile fabrication of highly efficient, stable, and hysteresis‐free tin oxide (SnO2)‐based PSCs is demonstrated with a cham...

This study aimed to classify biotypes in the same rhizobium species according to their phenotypic characteristics and the symbiotic efficiency between the alfalfa variety and rhizobium strain, and so to provide a knowledge base for breeding rhizobia that are effective symbiotic partners with alfalfa. Rhizobium strains were isolated from different p...

Development of a thin and dry electrode for electrocardiography (ECG) is essential in order to prevent skin irritation, allergic reactions from electrolytic gel, and motion artifacts caused by relative motion between the electrodes and the skin. In this study, we have developed a composite electrode made from Ag nanowires (AgNWs) and polyvinyl buty...

Transparent conducting electrodes (TCEs) have played a pivotal role in driving the continuous development of optoelectronics technologies, which include organic optoelectronic applications. In recent years, there has been a huge interest in designing innovative TCEs to replace the conventional indium tin oxide (ITO) electrodes, which suffer from co...

We investigated the effect of a compact TiO2 (c-TiO2) layer on the structural, optical, and performance characteristics of mesoporous perovskite solar cells (mp-PSCs) with fluorine-doped tin oxide (FTO)/mesoporous TiO2 with or without c-TiO2 layer/perovskite/spiro-OMeTAD/Au structure. The mp-PSCs with the c-TiO2 layer exhibited a dense and pinhole-...

A simple, cost-effective, and one-step procedure for fabrication of gold-nanoparticle-transition metal oxide (Au-TMO) thin films with tuned optical and structural properties is described. In this approach, a homogeneous mixed precursor solution was used to fabricate Au-MoO3 and Au-WO3 thin films via a spray pyrolysis technique. The in-situ grown Au...

In recent years, extensive research has been undertaken to develop fiber-shaped optoelectronic devices, because they are aesthetically pleasing, light in weight, and exhibit superior light emitting properties when compared with conventional planar analogues. In this work, we have successfully developed hollow-fiber shaped organic light emitting dio...

Electrical, optical, and structural characteristics of perovskite light‐emitting diodes (PeLEDs) are investigated. The PeLED consisting of ITO/ZnO/MAPbI3 (CH3NH3PbI3)/spiro‐OMeTAD/Ag structures shows a peak emission wavelength of 766 nm, turn‐on voltage of 1.7 V, reverse breakdown voltage of −5.4 V, current efficiency of 1.5 × 10−4 cdA−1, maximum l...

In this study, we designed a highly flexible, mechanically robust Ag mesh/ITO composite transparent conducting electrode (TCE) integrated with a microlens array (MLA) to improve the light extraction of organic light-emitting diodes (OLEDs). The mechanical flexibility and durability of a flexible OLED based on a Ag mesh/ITO composite TCE were superi...

The authors investigated the silver nanowires (AgNWs) contact formed on p-GaN. Transmission line model applied to the AgNWs contact to p-GaN produced near ohmic contact with a specific contact resistance (ρ sc) of 10⁻1~10⁻4 Ωcm². Noticeably, the contact resistance had a strong bias-voltage (or current-density) dependence associated with a local jou...

In this paper, the improvement of the conductor temperature calculation algorithm is studied. The allowable current of the underground transmission line is determined by the conductor temperature limit. Usually to calculate the allowable current limit, the conductor temperature is assumed in the most worst environment condition. It is possible to i...

In this work, the effects of annealing temperature and time for one-step fabrication of mixed metal halide perovskite films were investigated. The photovoltaic performance of perovskite solar cells (PSCs) improved from 8.30 to 10.85% after being annealed at 100 °C for 10 min and exhibited negligible photocurrent hysteresis when prepared at an ambie...

We report on a one-step spray printing technique to fabricate large-area flexible electrodes using poly (3, 4-ethylene dioxythiophene)-polystyrene sulfonate (PEDOT:PSS) and polyester cloth. The H3PO4 treated PEDOT:PSS electrodes exhibit an enhanced capacitance, high rate capability and wide voltage window (0–1.6 V). The printed polyester/PEDOT:PSS...

Paper-based electronic devices are attracting considerable attention, because the paper platform has unique attributes such as flexibility and eco-friendliness. Here we report on what is claimed to be the firstly fully integrated vertically-stacked nanocellulose-based tactile sensor, which is capable of simultaneously sensing temperature and pressu...

Herein, a novel strategy is presented for enhancing light absorption by incorporating gold nanostars (Au NSs) into both the active layer of organic solar cells (OSCs) and the rear-contact hole transport layer (HTL) of perovskite solar cells (PSCs). We demonstrate that the power conversion efficiencies of OSCs and PSCs with embedded Au NSs are impro...

Tungsten-doped indium oxide (WIO) transparent conducting thin films, to be used in inverted organic solar cells (IOSCs), were prepared by a polymer-assisted solution (PAS) process. Tungsten has high Lewis acid strength and it is, therefore, a promising candidate dopant for formulating high-mobility transparent conducting oxides with high transmitta...

The effect of boron on the migration and colonization of rhizobia in Gannong No.5 alfalfa (Medicago sativa Gannong No.5) tissues and subsequently seedling growth were investigated by root drenching using two cyan fluorescent protein (CFP) tagged rhizobia; Ensifer meliloti 12531f (12531f) and Ensifer meliloti GN5f (gn5f) containing different boron c...

The effects of stomatal morphology on stomatal function and water use efficiency were compared between two Hosta varieties (Hosta ensata and Hosta plantaginea). The results showed that the stomatal density of Hosta ensata was much higher than that of Hosta plantaginea, but the stomatal aperture was slightly smaller than the latter. The obvious diff...

To realize transparent organic light-emitting diodes (OLEDs), a top electrode should have excellent optical, electrical, and mechanical properties. Conventionally, transparent conductive oxides and semi-transparent metal are widely used for transparent top electrodes, but they have several fundamental drawbacks. We herein report efficient large-are...

A new deep green-emitting material, a 3,5-bis(trifluoromethyl)phenylene-substituted iridium(III) complex, fac-tris[2-(3′,5′-bis(trifluoromethyl)biphenyl-3-yl)pyridine]iridium (Ir(mtfppy)3), was synthesized. Introducing bulky 3,5-bis(trifluoromethyl)phenylene to the metaposition of pyridyl-phenyl results in blue-shifted narrow emission compared to t...

A network structure consisting of nanomaterials with a stable structural support and charge path on a large area is desirable for various electronic and optoelectronic devices. Generally, network structures have been fabricated via two main strategies: (1) assembly of pre-grown nanostructures onto a desired substrate and (2) direct growth of nanoma...

In this report, we demonstrate that moisture/O2 in ambient air is the major issue for the photovoltaic performance degradation and severe photocurrent hysteresis of non-encapsulated planar-perovskite solar cells. Consequently, this leads to difficulty in determining the real power conversion efficiency (PCE). Upon longer storage time, the evidence...

A novel approach for the fabrication of ultra-smooth and highly bendable substrates consisting of metal grid-conducting polymers that are fully embedded into transparent substrates (ME-TCEs) was successfully demonstrated. The fully printed ME-TCEs exhibited ultra-smooth surfaces (surface roughness ~1.0 nm), were highly transparent (~90% transmittan...

Purpose: The purpose of this study is to evaluate the correlation between lymph node count (LNC) and survival and to evaluate whether lymph node ratio (LNR) which is related to LNC is a better predictor of survival for gastric cancer than the N category of UICC/AJCC through a multi-institutional cohort study. Methods: The study cohort included 3...

We report hybrid white organic light-emitting diodes (WOLEDs) made by combining FIrpic-based blue-emitting OLEDs and a printable red-emitting inorganic phosphor. The color conversion can be easily controlled by adjusting the thickness of the red phosphor. FIrpic-based phosphorescent OLEDs, with a 15-μm-thick phosphor layer, show warm white light em...

Organic light-emitting diodes (OLEDs) have successfully entered mobile-phone display market and large-size OLED TVs have also been available by overcomming many technical obstacles. However, novel and innovative technologies are still required for flexible, transparent, and high-resolution displays. For example, augmented reaility (AR) and virtual...

We demonstrated highly efficient OLEDs by incorporating ZnS nanodots on top of a glass substrate via a chemical bath deposition process. The device efficiency of OLEDs with ZnS nanodot arrays was 1.26 times higher than that of OLEDs without ZnS. This enhancement in device efficiency is attributed to the improved light out-coupling efficiency that i...

A flexible transparent electrode (TE) is fabricated by thermal pressing of a metal-grid into a plastic film. The metal-grid is prepared by electrohydrodynamic continuous jet printing, which easily provides a high aspect ratio for the printed lines. Embedding the high-aspect-ratio metal-grid results in a smooth surface morphology that promotes the u...

Methylammonium lead iodide perovskite solar cells (PSCs) based on a solution-processed ZnO electron transporting layer were systematically investigated at low-temperature operating conditions. The power conversion efficiency gradually improved from 14.2% to 15.5% as the temperature decreased from 298 to 253 K, mainly owing to increments of short ci...

The effects of the gold nanoparticles (Au NPs) on performance of organic solar cells (OSCs) are systematically investigated based on blend of the low band gap polymer and fullerene. The localized surface plasmon resonance (LSPR) induced by the Au NPs enhance the light absorption in the active layer and the photoluminescence spectra showed a signifi...

Highly efficient, solution-processed, deep-blue fluorescent emitters are urgently required to realize inexpensive organic light-emitting diodes (OLEDs) for full-color displays and lighting applications. Herein, two new bipolar fluorescent emitters: 2-(4-(7-(9,9-dimethylacridin-10(9H)-yl)-9,9-diethyl- 9H-fl uoren-2-yl)phenyl)-1-phenyl-1H-phenanthro[...

We have fabricated transparent inverted organic light-emitting diodes (OLEDs) using a metal mesh embedded conductive film (MEF) with a non-metal transparent conductor and a novel vacuum lamination method. The device with the proposed electrode exhibits higher transmittance, lower reflectance, and especially much more stable optical properties than...

The aim of this study was to explore the salt resistance and physiological regulation mechanisms induced by exogenous 2,4-epibrassinolide (EBR) in alfalfa (Medicago sativa) seedlings. The effect of EBR on photosynthetic pigment contents, gas exchange parameters, and ion uptake, transport, and disputation in seedlings of M. sativa cv. Zhongmu No.3 a...

Highly efficient and air-stable inverted organic solar cells (IOSCs) were fabricated from solution-processed non-conjugated polyethylenimine ethoxylated (PEIE) as the polyelectrolyte, a zinc oxide (ZnO) bilayer as the electron transport layer, and an active layer of thieno[3,4-b]thiophene/benzodithiophene (PTB7) and [6,6]-phenyl-C71-butyric acid me...

A simple low-temperature solution processed of bismuth-doped ZnO nanorods (NRs) and poly(3-hexylthiophene) (P3HT) were used as electron acceptor and donor, respectively, in a hybrid inorganic-organic photovoltaic system. Control of the Bi precursor concentration via solution processing (hydrothermal method) plays an important role in altering the m...

In order to explore the comparation of injury on leaf adaxial and abaxial sides in Hosta plantaginea induced by ozone, micro-observation, chlorophyll fluorescent, gas exchange characteristics and chlorophyll content were studied in H. plantaginea seedlings under various ozone levels. Our micro-observation showed that injury symptoms on leaf adaxial...

This dissertation is a collection of three essays on information economics. The first essay, “Budget Constraint and Information Transmission in Multidimensional Decision Making,” illustrates how a constraint on a receiver’s actions impedes information transmission from multiple senders. The constraint causes an endogenous conflict of interest betwe...

Silver nanowires (AgNWs) have been successfully demonstrated to function as next-generation transparent conductive electrodes (TCEs) in organic semiconductor devices owing to their figures of merit, including high optical transmittance, low sheet resistance, flexibility, and low-cost processing. In this article, high-quality, solution-processed AgN...