• Journal of Adhesion and Interface
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• v.23 no.2
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• pp.39-43
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• 2022

In optoelectronic devices including displays and solar cells that convert electricity into light or light into electricity, it is important to control optical behavior of light to improve device efficiency. Specifically, the control of internal emitting light in the OLEDs can induce more light to go out, improving luminous efficiency. In addition, the control of optical behavior of incident light in solar cells can increase optical path in the light absorption layer, increasing power-conversion efficiency. In this study, we generated wrinkles as a physical structure to control optical behavior of light and independently controlled their wavelength and height by changing stress relaxation time. To explore the effect of wavelength and height on optical behavior, we conducted UV/Vis spectroscopy analysis of wrinkles with various heights at a constant wavelength or various wavelengths at a comparable height, figuring out a wrinkle with high aspect ratio has more dispersive light and less straight light. It indicates that high aspect ratio is required to change the optical behavior and increase the optical path.

• Current Photovoltaic Research
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• v.10 no.2
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• pp.39-48
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• 2022

A Se-containing Cu/SnSe₂/ZnSe precursor was employed to introduce S to the precursor to form Cu₂ZnSn(S,Se)₄ (CZTSSe) film. The morphology of CZTSSe films strongly varied with two different pre-annealing environments: S and N₂. The CZTSSe film with S pre-annealing showed a dense morphology with a smooth surface, while that with N₂ pre-annealing showed a porous film with a plate-shaped grains on the surface. CuS and Cu₂Sn(S,Se)₃ phases formed during the S pre-annealing stage, while SnSe and Cu₂SnSe₃ phases formed during the N₂ pre-annealing stage. The SnSe phase formed during N₂ pre-annealing generated SnS₂ phase that had plate shape and severely aggravated the morphology of CZTSSe film. The power conversion efficiency of the CZTSSe solar cell with S pre-annealing was low (1.9%) due to existence of Zn(S.Se) layer between CZTSSe and Mo substrate. The results indicated that S pre-annealing of the precursor was a promising method to achieve a good morphology for large area application.

• Korean Journal of Materials Research
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• v.32 no.10
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• pp.419-424
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• 2022

Halide perovskite solar cells (PSCs) have improved rapidly over the past few years, and research on the optoelectrical properties of halide perovskite thin films has grown as well. Among the characterization techniques, photoluminescence (PL), a method of collecting emitted photons to evaluate the properties of materials, is widely applied to evaluate improvements in the performance of PSCs. However, since only photons emitted from the film in the escape cone are included, the photons collected in PL are a small fraction of the total photons emitted from the film. Unlike PSCs power conversion efficiency, PL measuring methods have not been standardized, and have been evaluated in a variety of ways. Thus, an in-depth study is needed of the methods used to evaluate materials using PL spectra. In this study, we examined the PL spectra of the perovskite light harvesting layer with different measurement protocols and analyzed the features. As the incident angle changed, different spectra were observed, indicating that the PL emission spectrum can depend on the measuring method, not the material. We found the intensity and energy of the PL spectra changes were due to the path of the emitted photons. Also, we found that the PL of halide perovskite thin films generally contains limited information. To solve this problem, the emitted photons should be collected using an integrating sphere. The results of this study suggest that the emission spectrum of halide perovskite films should be carefully interpreted in accordance with PL measuring method, since PL data is mostly affected by the method.

• Current Photovoltaic Research
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• v.11 no.3
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• pp.67-74
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• 2023

The earth-abundant element-based Cu₂ZnSn(S,Se)₄ (CZTSSe) thin film solar cells (TFSCs) have attracted greater attention in the photovoltaic (PV) community due to their rapid development in device power conversion efficiency (PCE) >13%. In the present work, we demonstrated the fine-tuning of the bandgap in the CZTSSe TFSCs by altering the sulfur (S) to the selenium (Se) chalcogenide ratio. To achieve this, the CZTSSe absorber layers are fabricated with different S/(S+Se) ratios from 0.02 to 0.08 of their weight percentage. Further compositional, morphological, and optoelectronic properties are studied using various characterization techniques. It is observed that the change in the S/(S+Se) ratios has minimal impact on the overall Cu/(Zn+Sn) composition ratio. In contrast, the S and Se content within the CZTSSe absorber layer gets altered with a change in the S/(S+Se) ratio. It also influences the overall absorber quality and gets worse at higher S/(S+Se). Furthermore, the device performance evaluated for similar CZTSSe TFSCs showed a linear increase and decrease in the open circuit voltage (V_oc) and short circuit current density (J_sc) of the device with an increasing S/(S+Se) ratio. The external quantum efficiency (EQE) measured also exhibited a linear blue shift in absorption edge, increasing the bandgap from 1.056 eV to 1.228 eV, respectively.

• Journal of Animal Science and Technology
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• v.65 no.2
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• pp.351-364
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• 2023

The experiment was carried out to study the effect of Korean wild ginseng adventitious root supplementation on the laying performance, egg quality, cytokine expression, ginsenoside concentration, and microflora quantity of Institut de selection Animale (ISA) brown laying hens at 24 weeks old. A total of 90 laying hens were subjected to a completely randomized design at three treatments, five repetitions and six laying hens per replicate. The experiments were divided by diets into the basic feed (CON), basic feed + 0.1% wild ginseng (WG1), and basic feed + 0.5% wild ginseng (WG2). The feeding trial was carried out over a duration of 12 weeks after an initial acclimation period of 2 weeks. Feeds and water were administered ad libitum in mash form, and light was available for 16 hours per day. At the end of study, henday egg production (HDEP), average egg weight (AEW), and egg mass (EM) were increased (p <0.05) in WG2 at week 12. Feed conversion ratio (FCR) was decreased (p < 0.05) in WG2 at week 12. The ginsenoside content in egg yolk was increased (p <0.05) in laying hens in the WG2 treatment at week 12. Relative expression of tumor necrosis factor alpha (TNF-α) was reduced (p < 0.05) in the WG supplemented diets at week 12. The fecal microflora quantity of Lactobacillus was increased (p < 0.05) in WG2 at week 8 to week 12, and Escherichia coli (E. coli) was significantly decreased (p < 0.05) in the WG2 at week 12. We concluded that the result observed in the HDEP, AEW, EM and FCR was due to an increase in ginsenoside content, leading to an improvement in the TNF-α, and fecal microflora quantity such as Lactobacillus and E. coli in the WG2 supplemented diets. We therefore recommend the use of WG at application level 0.5% per basal diet for optimum laying performance in layer hens.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.1
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• pp.1-16
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• 2023

Recently, the shift to next-generation wide-bandgap (WBG) power semiconductor for electric vehicle is accelerated due to the need to improve power conversion efficiency and to overcome the limitation of conventional Si power semiconductor. With the adoption of WBG semiconductor, it is also required that the packaging materials for power modules have high temperature durability. As an alternative to conventional high-temperature Pb-based solder, Ag sintering die attach, which is one of the power module packaging process, is receiving attention. In this study, we will introduce the recent research trends on the Ag sintering die attach process. The effects of sintering parameters on the bonding properties and methodology on the exact physical properties of Ag sintered layer by the realization 3D image are discussed. In addition, trends in thermal shock and power cycle reliability test results for power module are discussed.

• Journal of Electrochemical Science and Technology
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• v.14 no.1
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• pp.96-104
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• 2023

Synergistically increased oxygen evolution reaction (OER) of manganese oxide (MnO₂) catalyst is introduced with surface-modified halloysite nanotube (Fe₃O₄-HNTs) structure. The flake shaped MnO₂ catalyst is attached on the nanotube template (Fe₃O₄-HNTs) by series of wet chemical and hydrothermal method. The strong interaction between MnO₂ and Fe₃O₄-HNTs maximized active surface area and inter-connectivity for festinate charge transfer reaction for OER. The synergistical effect between Fe₃O₄ layer and MnO₂ catalyst enhance the Mn³⁺/Mn⁴⁺ ratio by partial replacement of Mn ions with Fe. The relatively increased Mn³⁺/Mn⁴⁺ ratio on MnO₂@FHNTs induced 𝜎^* orbital (e_g) occupation close to single electron, improving the OER performances. The MnO₂@FHNTs catalyst exhibited the reduced overpotential of 0.42 V (E vs. RHE) at 10 mA/cm² and Tafel slope of (99 mV/dec), compared with that of MnO₂ with unmodified HNTs (0.65 V, 219 mV/dec) and pristine MnO₂ (0.53 V, 205 mV/dec). The present study provides simple and innovative method to fabricate nano fiberized OER catalyst for a broad application of energy conversion and storage systems.

• Journal of Electrochemical Science and Technology
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• v.15 no.1
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• pp.96-110
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• 2024

Polymer electrolyte membrane fuel cells (PEMFCs) are green energy conversion devices, for which commercial markets have been established, owing to their application in fuel cell vehicles (FCVs). Development of cathode electrocatalysts, replacing commercial Pt/C, plays a crucial role in factors such as cost reduction, high performance, and durability in FCVs. PtNi octahedral catalysts are promising for oxygen reduction reactions owing to their significantly higher mass activity (10-15 times) than that of Pt/C; however, their application in membrane electrode assemblies (MEAs) is challenged by their low stability. To overcome this durability issue, various approaches, such as third-metal doping, composition control, halide treatment, formation of a Pt layer, annealing treatment, and size control, have been explored and have shown promising improvements in stability in rotating disk electrode (RDE) testing. In this review, we aimed to compare the features of each strategy in terms of enhancing stability by introducing a stability improvement factor for a direct and reasonable comparison. The limitations of each strategy for enhancing stability of PtNi octahedral are also described. This review can serve as a valuable guide for the development of strategies to enhance the durability of octahedral PtNi.

• Applied Chemistry for Engineering
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• v.35 no.2
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• pp.128-133
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• 2024

Although antisolvent-assisted crystallization is one of the promising processes to produce high-quality perovskite films, general antisolvents such as chlorobenzene (CB) have toxic and volatile properties. In addition, CB is not suitable to control the crystallization of perovskite in the atmospheric air. In this work, isopropyl acetate (IA) is used as an eco-friendly antisolvent to demonstrate air-processed perovskite solar cells, and ethyl-4-cyanocinnamate (E4CN) with a cyano group, carbonyl group, and aromatic ring is introduced in IA to improve the performance and stability of devices. Defects at the surface and grain boundaries of the perovskite layer, such as un-coordinated Pb²⁺ and iodine, can be decreased resulting from the interaction of E4CN and perovskite, and thus reduced recombination and enhanced carrier transport can be expected. As a result, the perovskite device with E4CN achieves a high maximum power conversion efficiency (PCE) of 18.89% and outstanding stability, maintaining 60% of the initial efficiency for 300 h in the air without any encapsulation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.1-7
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• 2017

Cobalt silicide was used as a counter electrode in order to confirm its reliability in dye-sensitized solar cell (DSSC) devices. 100 nm-Co/300 nm-Si/quartz was formed by an evaporator and cobalt silicide was formed by vacuum heat treatment at $700^{\circ}C$ for 60 min to form approximately 350 nm-CoSi. This process was followed by etching in $80^{\circ}C$-30% $H_2SO_4$ to remove the cobalt residue on the cobalt silicide surface. Also, for the comparison against Pt, we prepared a 100 nm-Pt/glass counter electrode. Cobalt silicide was used for the counter electrode in order to confirm its reliability in DSSC devices and maintained for 0, 168, 336, 504, 672, and 840 hours at $80^{\circ}C$. The photovoltaic properties of the DSSCs employing cobalt silicide were confirmed by using a simulator and potentiostat. Cyclic-voltammetry, field emission scanning electron microscopy, focused ion beam scanning electron microscopy, and energy dispersive spectrometry analyses were used to confirm the catalytic activity, microstructure, and composition, respectively. The energy conversion efficiency (ECE) as a function of time and ECE of the DSSC with Pt and CoSi counter electrodes were maintained for 504 hours. However, after 672 hours, the ECEs decreased to a half of their initial values. The results of the catalytic activity analysis showed that the catalytic activities of the Pt and CoSi counter electrodes decreased to 64% and 57% of their initial values, respectively(after 840 hours). The microstructure analysis showed that the CoSi layer improved the durability in the electrolyte, but because the stress concentrates on the contact surface between the lower quartz substrate and the CoSi layer, cracks are formed locally and flaking occurs. Thus, deterioration occurs due to the residual stress built up during the silicidation of the CoSi counter electrode, so it is necessary to take measures against these residual stresses, in order to ensure the reliability of the electrode.