Jae-Seong Jeong

Estimation of the degradation rate of multi-crystalline silicon photovoltaic module under thermal cycling stress

Abstract The overall power of an outdoor-exposed photovoltaic (PV) module decreases as a result of thermal cycling (TC) stress, due to the formation of cracks between the solder and metal. In this study, the thermal fatigue life of solder (62Sn36Pb2Ag) interconnection between copper and silver metallization in PV module was studied. This paper describes in detail the degradation rate ( R D ) prediction model of solder interconnection for crystalline PV module. The R D prediction model is developed which based on published constitutive equations for solder and TC test results on actual PV module. The finite element method was employed to study the creep strain energy density of solder interconnections in TC conditions. Three types of accelerated tests were conducted to determine the prediction model parameters. R D in benchmark condition is predicted and compared with those of TC conditions.

Stress Mechanism about Field Lightning Surge of High Voltage BJT Based Line Driver for ADSL System

Abstract In this paper, we have verified stress root caused by lightning surge in High voltage BJT based line driver of ADSL telecommunication and created failure mechanism. To reproduce damages in Line driver, we have applied STD surge waveform in operating condition, which is specified in IEC-6000-4-5, to component and board level. Visual isolation for Damage root was conducted with Real-time Electrical Stress Analysis (RTESA) utilizing Photon Emission Microscopy (PEM). The surge made with input of Tx output created junction breakdown of amplifier, which is made of HVBJT cells, and also caused current crowding from Vcc (supply voltage). In case of Positive pulse, current crowding was observed from between Collector and Vcc (+)12V. For negative pulse, at between Emitter and Vee (−)12V, current crowding was found. For both cases, device damage level was the same. All of these could be considered as transient latchup phenomenon created in BJT cell. Applying temporary clamping diode to line driver Tx, we have conducted Board level surge injection test. As a result, with the correlation between surge level from component level reproduction test and the one from system level, we have decided field lightning surge damage level and set up line driver protection margin.

Effect of aspect ratio on the uptake and toxicity of hydroxylated-multi walled carbon nanotubes in the nematode, Caenorhabditis elegans.

Objectives In this study, the effect of tube length and outer diameter (OD) size of hydroxylated-multi walled carbon nanotubes (OH-MWCNTs) on their uptake and toxicity was investigated in the nematode Caenorhabditis elegans using a functional mutant analysis. Methods The physicochemical properties of three different OH-MWCNTs were characterized. Uptake and toxicity were subsequently investigated on C. elegans exposed to MWCNTs with different ODs and tube lengths. Results The results of mutant analysis suggest that ingestion is the main route of MWCNTs uptake. We found that OH-MWCNTs with smaller ODs were more toxic than those with larger ODs, and OH-MWCNTs with shorter tube lengths were more toxic than longer counterparts to C. elegans. Conclusions Overall the results suggest the aspect ratio affects the toxicity of MWCNTs in C. elegans. Further thorough study on the relationship between physicochemical properties and toxicity needs to be conducted for more comprehensive understanding of the uptake and toxicity of MWCNTs.

Field discoloration analysis and UV/temperature accelerated degradation test of EVA for PV

For more than 25 years of lifetime of Photovoltaic (PV) module, the importance of the study about the durability of PV module component is getting higher and higher. Ethylene Vinyl Acetate (EVA), Polymer encapsulation, is one of the important components to protect the cell and improve optical transmittance. Therefore, the study about improving the durability through long term degradation characteristic of E VA based on the environmental stress is essential. This study investigates discoloration degradation mechanism of E VA under Ultraviolet (UV) and temperature complex environmental stress. Chemical/physical change of 25 year-old EVA years was analyzed. Similar amount of UV/Temp acceleration condition which was induced to E VA for 25 years design. After Acceleration Degradation Test (ADT), degradation characteristics were analyzed by using SEM, FT-IR, TGA, and DSC. The result was compared with field-aged EVA.

Lifetime prediction model of thermal fatigue stress on crystalline silicon photovoltaic module

Thermal cycling stress can result in fatigue cracks of interconnections between ribbon wires and the metallization of a photovoltaic (PV) module, thereby increasing its series resistance. Therefore, in this study, the thermal cycling (TC) history of PV modules exposed to two benchmark climate (Phoenix, AZ) has been derived employing corresponding meteorological data. Using the three parameters rain-flow counting algorithm, the number of TCs versus temperature change was calculated over one year. The number of rain-flow cycles was 935 in Phoenix. Furthermore, three types of accelerated tests were conducted to develop a lifetime prediction model. The Basquin equation was used to predict the number of cycles to failure, based on stress calculation. A finite element model for stress analysis was developed. Failure analysis shows that crack occurred at the solder joint after accelerated test.

Field failure mechanism and reproduction due to moisture for low-voltage ZnO varistors

Abstract This paper presents an investigation of the insulation resistance/leakage current failure of low-voltage ZnO varistors in the field. Failed varistors resumed normal operation after surface polishing, and the fault site was located in the Si coating layer and the outermost side of the bulk ZnO. To reproduce the field failure phenomenon, an effective stress that causes failure was suggested. Accelerated reproduction tests were conducted to determine if the chosen stress caused the field failure. To accelerate the formation of the defect, a water precipitation/reflow precondition was applied. A biased HAST after preconditioning could reproduce the same field failure phenomenon. The failure mechanism and root cause were determined by comparison with a sample that used an improved coating method. A failure mechanism was proposed in which the insulation resistance degradation was caused by Zn(OH) 2 , which is generated by moisture absorbed into the surface of the varistor. Further, the ZnO and leakage current degradation was caused by H + ions generated by dissociation of the diffused H 2 O to the ZnO grain boundaries on the surface of the bulk ceramic. Finally, the effective factors for field failure of the ZnO varistor were defined as the weakness of the Si coating, moisture ingress, and bias.

JAK/STAT and TGF-ß activation as potential adverse outcome pathway of TiO 2 NPs phototoxicity in Caenorhabditis elegans

Titanium dioxide nanoparticles (TiO2NPs) are widely used nanoparticles, whose catalytic activity is mainly due to photoactivation. In this study, the toxicity of TiO2NPs was investigated on the nematode Caenorhabditis elegans, with and without UV activation. Comparative analyses across the four treatments revealed that UV-activated TiO2NPs led to significant reproductive toxicity through oxidative stress. To understand the underlying molecular mechanism, transcriptomics and metabolomics analyses were conducted, followed by whole-genome network-based pathway analyses. Differential expression analysis from microarray data revealed only 4 DEGs by exposure to TiO2NPs alone, compared to 3,625 and 3,286 DEGs by UV alone and UV-activated TiO2NPs, respectively. Pathway analyses suggested the possible involvement of the JAK/STAT and TGF-ß pathways in the phototoxicity of TiO2NPs, which correlated with the observation of increased gene expression of those pathways. Comparative analysis of C. elegans response across UV activation and TiO2NPs exposure was performed using loss-of-function mutants of genes in these pathways. Results indicated that the JAK/STAT pathway was specific to TiO2NPs, whereas the TGF-ß pathway was specific to UV. Interestingly, crosstalk between these pathways was confirmed by further mutant analysis. We consider that these findings will contribute to understand the molecular mechanisms of toxicity of TiO2NPs in the natural environment.

Global metabolomics approach in in vitro and in vivo models reveals hepatic glutathione depletion induced by amorphous silica nanoparticles

The present study aimed to investigate the mechanisms involved in amorphous silica nanoparticles (aSiNPs)-mediated hepatotoxicity through the evaluation of changes in global metabolomics in in vitro and in vivo systems. 1H NMR-based non-targeted global metabolomics and biochemical approaches were conducted in an aSiNPs-treated human hepatoma cell line (HepG2) and in ICR mice liver. The non-targeted NMR-based metabolomic analysis, followed by pathway analysis, revealed the perturbation of glutathione metabolism and the depletion of the glutathione pool after aSiNPs treatment in both in vitro (HepG2 cells) and in vivo systems. The total glutathione level, glutathione-S-transferase enzyme activity, and antioxidant gene expression strongly corroborated the metabolomic analysis results. The in vitro results were further supported by the in vivo data, specifically for metabolites profiling (Pearson Correlation coefficient is 0.462 (p = 0.026)). Furthermore, the depletion of glutathione, the formation of NADPH oxidase-mediated reactive oxygen species, and oxidative stress were evident in aSiNPs-treated HepG2 cells. Overall, the suppression of glutathione metabolism and oxidative stress are among the principal causes of aSiNPs-mediated hepatotoxicity.

Lifetime and failure analysis of perovskite-based ceramic NTC thermistors by thermal cycling and abrasion combined stress

Abstract A perovskite-based ceramic NTC (negative temperature coefficient) thermistor was developed. A ceramic NTC thermistor was used for sensing the temperature of the heated roller from a laser printer. FMEA (failure mode and effect analysis) was applied to find the effective stress factor on the reliability of the sensor. System failure caused by the malfunction of a thermistor was studied. Possible failure modes, effective stresses that can lead to shortened lifetimes, and potential weak points of the thermistor were analyzed. The combined stress of thermal cycling and abrasion was found to be the most important factor among the listed effective stresses. The temperature profile of the thermal cycle was designed by taking into account the actual operating conditions, and an accelerated lifetime testing machine for estimating operational lifetimes was developed for the profile with a roller rotation. The lifetime of thermistor was estimated from the duration frequency of the thermal cycle using a lifetime testing machine with a roller rotation.

TID and SEL Testing on PWM-IC Controller of DC/DC Power Buck Converter

DC/DC switching power converters are commonly used to generate a regulated DC output voltage with high efficiency. The DC/DC converter is composed of a PWM-IC (pulse width modulation-integrated circuit) controller, a MOSFET (metal-oxide semiconductor field effect transistor), inductor, capacitor, etc. It is shown that the variation of threshold voltage and the offset voltage in the electrical characteristics of PWM-IC increase by radiation effects in TID (Total Ionizing Dose) testing at the low energy rays using , and 4 heavy ions applied for SEL (Single Event Latch-up) make the PWM pulse unstable. Also, the output waveform for the given input in the DC/DC converter is observed by the simulation program with integrated circuit emphasis (SPICE). TID testing on PWM-IC is accomplished up to the total dose of 30 krad, and the cross section() versus LET() in the PWM operation is studied at SEL testing after implementation of the controller board.