Hyomin Park

Release of nisin from various heat-pressed and cast films

Nisin-incorporated biopolymers (methylcellulose (MC), hydroxypropylmethyl cellulose (HPMC), κ-carrageenan and chitosan) films made by heat-press and casting methods were investigated. For quantitative determinations of nisin release in both categories of prepared films, the plate diffusion method was employed using Micrococcus luteus ATCC 10240 as the test microorganism. Cast films exhibited larger inhibitory zones overall when compared with that of the heat-pressed method. Among all the nisin-incorporated films assayed, the antimicrobial activity was most effective in MC films in the heat-pressed category and chitosan films in the cast films category.

UV Degradation and Recovery of Perovskite Solar Cells

Although the power conversion efficiency of perovskite solar cells has increased from 3.81% to 22.1% in just 7 years, they still suffer from stability issues, as they degrade upon exposure to moisture, UV light, heat, and bias voltage. We herein examined the degradation of perovskite solar cells in the presence of UV light alone. The cells were exposed to 365 nm UV light for over 1,000 h under inert gas at <0.5 ppm humidity without encapsulation. 1-sun illumination after UV degradation resulted in recovery of the fill factor and power conversion efficiency. Furthermore, during exposure to consecutive UV light, the diminished short circuit current density (Jsc) and EQE continuously restored. 1-sun light soaking induced recovery is considered to be caused by resolving of stacked charges and defect state neutralization. The Jsc and EQE bounce-back phenomenon is attributed to the beneficial effects of PbI2 which is generated by the decomposition of perovskite material.

Solution properties and PGSE-NMR self-diffusion study of C18:1E10/oil/water system

The microemulsion systems of polyoxyethylene-10-oleyl ether/oil/water have been studied. The medium chain triglycerides (MCT) and retinyl palmitate mixture (1:1, w/w) was solubilized up to 9% w/w at the surfactant concentration of 25% w/w. The lowest phase inversion temperature (PIT) of the microemulsion solutions was about 57 8C and showed no phase separation for 6 months at room temperature. The critical micelle concentration (CMC) of polyoxyethylene-10-oleyl ether (C18:1E10) was 1.20/10 5 Ma t 278C. The phase behavior and pulsed field gradient NMR data clearly indicate that these microemulsions are discrete oil-in-water (O/W) microemulsions. The self-diffusion coefficient of free retinyl palmitate, MCT and MCT/retinyl palmitate mixture (1:1, w/w) were 1.61/10 10 , 2.60/ 10 10 and 2.59/10 10 m 2 s 1 , respectively. The D of free C18:1E10 was 4.96/10 11 m 2 s 1 . The relative selfdiffusion coefficients of water and oil differed by more than 1 order of magnitude. The hydrodynamic radius (RH )o f this oil swollen micelle was calculated as 14 nm at 1% w/w oil concentration (23% w/w C18:1E10, 0.5% w/w MCT, 0.5% w/w retinyl palmitate, 76% w/w water) and increased to 34 nm at 7% w/w oil concentration (23% w/w C18:1E10, 3.5% w/ w MCT, 3.5% w/w retinyl palmitate, 70% w/w water). # 2002 Elsevier Science B.V. All rights reserved.

Improvement of electrical properties in screen-printed crystalline silicon solar cells by contact treatment of the grid edge

In this study, the influence of HF treatment of Ag pastes after a firing process was investigated. It was shown that the HF treatment can improve the fill factors and efficiencies of various cells including those with high initial specific contact resistances. SEM images showed that this improvement is due to the etching of the thin glass layer at the Ag-Si boundary, which exposes the Ag crystallites and colloids. These colloids electrically connect the bulk Ag to the Si through a direct contact, which reduces both the transfer length and the specific contact resistance. A model of the current path was proposed to explain the effect of HF treatment on the edge of the Ag grid.

Liquid chromatography-tandem mass spectrometry determination of N-nitrosamines released from rubber or elastomer teats and soothers

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method as an alternative to a gas chromatography-thermal energy analyser (GC-TEA) method recommended by the European Committee on Standardization (CEN) was validated for the simultaneous determination of eight N-nitrosamines released into artificial saliva from rubber or elastomer teats and soothers. N-nitroso-dipropylamine-d14 (NDPA-d14) was used as internal standard for accurate quantification. The method was validated with relatively good analytical results, including sufficiently low limits of detection (0.1–2 µg kg−1 of sample) and good linearity (r 2 > 0.99) throughout the studied concentration ranges. Intra- and inter-day precisions expressed with the relative standard deviation (RSD, %) were 3.4–8.0% and 4.4–11.3%, which were below the performance criteria based on one-half of the value derived from the Horwitz value. It was also found that the LC-MS/MS method is sufficiently rugged and successfully applicable to its routine analysis for the compliance test of Commission Directive 93/11/EEC.

Effects of Current-injection Firing with Ag Paste in a Boron Emitter

A high contact resistance for screen-printed contacts was observed when a conventional Ag paste was used on a boron emitter. The results of this study suggest that electron injection during firing is one of the processes that contribute to a lower contact resistance. Larger quantities of Ag precipitates formed upon electron injection into the boron emitter, which was confirmed by observing Ag crystallite or dendrite structures on the boron and by measuring the contact resistance between the boron emitter and the Ag bulk. The electron-injected sample had approximately 10000 times lower contact resistance than an untreated sample. The contact resistance of the electron-injected sample was 0.021 mΩ∙cm2 under optimal conditions, which is lower than that of conventional p-type silicon solar cells. Thus, electron injection can effectively lower contact resistance when using Ag paste in n-type silicon solar cells. During the cooling in the firing process, dissolved Ag ions in the glass layer are formed as dendrites or crystallites/particles. The dendrites are formed earlier than others via electrochemical migration under electron injection conditions. Then, crystallites and particles are formed via a silicon etching reaction. Thus, Ag ions that are not formed as dendrites will form as crystallites or particles.

Effect of the Phosphorus Gettering on Si Heterojunction Solar Cells

To improve the efficiency of crystalline silicon solar cells, should be collected the excess carrier as much as possible. Therefore, minimizing the recombination both at the bulk and surface regions is important. Impurities make recombination sites and they are the major reason for recombination. Phosphorus (P) gettering was introduced to reduce metal impurities in the bulk region of Si wafers and then to improve the efficiency of Si heterojunction solar cells fabricated on the wafers. Resistivity of wafers was measured by a four-point probe method. Fill factor of solar cells was measured by a solar simulator. Saturation current and ideality factor were calculated from a dark current density-voltage graph. External quantum efficiency was analyzed to assess the effect of P gettering on the performance of solar cells. Minority bulk lifetime measured by microwave photoconductance decay increases from 368.3 to 660.8 μs. Open-circuit voltage and short-circuit current density increase from 577 to 598 mV and 27.8 to 29.8 mA/cm2, respectively. The efficiency of solar cells increases from 11.9 to 13.4%. P gettering will be feasible to improve the efficiency of Si heterojunction solar cells fabricated on P-doped Si wafers.

Correction to: Optimization of Controllable Factors in the Aluminum Silicon Eutectic Paste and Rear Silicon Nitride Mono-Passivation Layer of PERC Solar Cells

The original version of this article unfortunately contained a mistake. The acknowledgements section was incomplete. The correct information is given below.

Effects of Laser Doping on Selective Emitter Si Solar Cells

Laser-doped selective emitter process requires dopant source deposition, spin-on-glass, and is able to form selective emitter through SiNx layer by laser irradiation on desired locations. However, after laser doping process, the remaining dopant layer needs to be washed out. Laser-induced melting of pre-deposited impurity doping is a precise selective doping method minimizing addition of process steps. In this study, we introduce a novel scheme for fabricating highly efficient selective emitter solar cell by laser doping. During this process, laser induced damage induces front contact destabilization due to the hindrance of silver nucleation even though laser doping has a potential of commercialization with simple process concept. When the laser induced damage is effectively removed using solution etch back process, the disadvantage of laser doping was effectively removed. The devices fabricated using laser doping scheme power conversion efficiency was significantly improved about 1% abs. after removal the laser damages.

Effects of Firing Ambient on Rear Metallization for Silicon Solar Cells

【For rear metallization with Al paste, Al back contacts require good passivation, high reflectance, and a processing temperature window compatible with the front metal. In this paper, the effect of the firing ambient during the metallization process on the formation of Al rear metal was investigated. We chose three different gases as ambient gases during the firing process. Using SEM, we observed the formation of a back surface field in