Hye-Jeong Park

Optimization of an Electron Transport Layer to Enhance the Power Conversion Efficiency of Flexible Inverted Organic Solar Cells

The photovoltaic (PV) performance of flexible inverted organic solar cells (IOSCs) with an active layer consisting of a blend of poly(3-hexylthiophene) and [6, 6]-phenyl C61-butlyric acid methyl ester was investigated by varying the thicknesses of ZnO seed layers and introducing ZnO nanorods (NRs). A ZnO seed layer or ZnO NRs grown on the seed layer were used as an electron transport layer and pathway to optimize PV performance. ZnO seed layers were deposited using spin coating at 3,000 rpm for 30 s onto indium tin oxide (ITO)-coated polyethersulphone (PES) substrates. The ZnO NRs were grown using an aqueous solution method at a low temperature (90°C). The optimized device with ZnO NRs exhibited a threefold increase in PV performance compared with that of a device consisting of a ZnO seed layer without ZnO NRs. Flexible IOSCs fabricated using ZnO NRs with improved PV performance may pave the way for the development of PV devices with larger interface areas for effective exciton dissociation and continuous carrier transport paths.

Low-temperature growth and characterization of ZnO thin films for flexible inverted organic solar cells

Flexible inverted organic solar cells (IOSCs) with a zinc oxide (ZnO) thin film layer acting as an effective electron transport layer and a low reflective light absorber were fabricated in this study. The high quality ZnO thin films on flexible indium tin oxide-coated polyethersulfone (PES) substrates were grown in a non-vacuum process using mist pyrolysis chemical vapor deposition at a low temperature of 180 °C without any thermal damage to the PES substrate. The power conversion efficiency of the flexible IOSCs with ZnO thin films averaged 3.1% at a simulated air-mass of 1.5 global full-sun (100 mW cm−2) illumination, which was greater than that of flexible IOSCs with a ZnO thin film formed using a sol–gel method (approximately 2.3%).

The Relationship between 10-Year Cardiovascular Risk Calculated Using the Pooled Cohort Equation and the Severity of Non-Alcoholic Fatty Liver Disease

Background We investigated the association between the severity of non-alcoholic fatty liver disease (NAFLD) and the estimated 10-year risk of cardiovascular disease (CVD) calculated by Pooled Cohort Equation (PCE) and Framingham risk score (FRS). Methods A total of 15,913 participants (mean age, 46.3 years) in a health screening program were selected for analysis. The presence and severity of fatty liver was assessed by abdominal ultrasonogram. Subjects who drank alcohol more than three times a week were excluded from the study. Results Among the participants, 57.6% had no NAFLD, 35.4% had grade I, 6.5% had grade II, and 0.5% had grade III NAFLD. Mean estimated 10-year CVD risk was 2.59%, 3.93%, 4.68%, and 5.23% calculated using the PCE (P for trend <0.01) and 4.55%, 6.39%, 7.33%, and 7.13% calculated using FRS, according to NAFLD severity from none to severe (P for trend <0.01). The odds ratio for ≥7.5% estimated CVD risk calculated using the PCE showed a higher correlation with increasing severity of NAFLD even after adjustment for conventional CVD risk factors (1.52, 2.56, 3.35 vs. the no NAFLD group as a reference, P<0.01) compared with calculated risk using FRS (1.65, 1.62, 1.72 vs. no NAFLD group as a reference, P<0.01). Conclusion In our study of apparently healthy Korean adults, increasing severity of NAFLD showed a higher correlation with estimated 10-year CVD risk when calculated using the PCE than when calculated using FRS.

Increased risk of subclinical atherosclerosis associated with high visceral adiposity index in apparently healthy Korean adults: the Kangbuk Samsung Health Study

Abstract Background: The visceral adiposity index (VAI) is a mathematical tool that reflects a patient’s visceral adiposity and insulin resistance. Recent studies have noted an association between VAI and cardiovascular event. We analyzed the association between VAI and coronary artery calcium score (CACS) in Korean adults. Methods: For 33,468 participants (mean age 42 yrs) in a health screening program, VAI was calculated using the following formulae: [waist circumference (WC)/{39.68 + (1.88 * body mass index (BMI))}] * (triglyceride/1.03) * {1.31/high-density lipoprotein cholesterol (HDL-C)} for men and [WC/{36.58 + (1.89 * BMI)}] * (triglyceride/0.81) * (1.52/HDL-C) for women. Coronary artery calcium scores were measured with multi-detector computed tomography. Results: CACS was positively correlated with VAI (r = 0.027, p < 0.001). Subjects with 0 < CACS <100 and CACS ≥ 100 had significantly higher VAI compared to those with CACS = 0 (2.04 ± 1.97, 2.08 ± 1.67 vs. 1.68 ± 1.50, p < 0.001). In logistic regression analyses with CACS >0 as the dependent variable, subjects in the highest tertile of VAI (>1.777) had significantly increased odds ratio for CACS >0 compared to subjects in the lowest tertile (<0.967), even after adjusting for confounding variables, including BMI (OR 1.26, 95% CI 1.147–1.381). Conclusions: Subjects with high VAI had increased risk for subclinical atherosclerosis, as assessed by CACS. Key messages Recent studies have noted an association between visceral adiposity index (VAI) and cardiovascular event. Subjects with coronary artery calcification (CAC) showed significantly higher VAI compared to those without CAC. The subjects with high VAI showed increased odds ratio for CAC as compared to subjects with low VAI, suggesting high VAI reflects increased risk for subclinical atherosclerosis

Increased association of coronary artery calcification in apparently healthy Korean adults with hypertriglyceridemic waist phenotype: The Kangbuk Samsung Health Study

BACKGROUND Hypertriglyceridemic waist phenotype is a simple screening parameter to identify people at increased risk for cardiovascular disease. We evaluated whether hypertriglyceridemic waist (HTGW) phenotype increases the risk for coronary artery calcification (CAC) in apparently healthy Korean adults. METHODS A total of 32,186 participants (mean age 41.3, 80.2% men) in a health screening program, in whom the coronary artery calcium score (CACS) was measured, were analyzed. Subjects were divided into four groups: 1) normal waist circumference (WC)-normal triglyceride (TG) (NWNT), 2) normal WC-high TG (NWHT), 3) enlarged WC-normal TG (EWNT), and 4) enlarged WC-high TG (EWHT). Enlarged WC was defined as WC ≥ 90 cm for men and ≥ 85 cm for women; high serum TG was defined as TG ≥ 150 mg/dL. The presence of CAC was defined by CACS >0, and CACS was analyzed in a logarithmized form of CACS plus 1 {ln(CACS+1)}. RESULTS A total of 14.9% of the participants had CAC. The EWHT group showed the highest mean value for ln(CACS+1) among the four groups. The EWHT group showed the highest odds ratio for CAC, with NWHT group the second, and with EWNT group the third compared with the NWNT group after adjusting for confounding variables (1.579, 1.302, and 1.266 vs. NWNT). CONCLUSIONS The EWHT group showed the highest association for CAC, suggesting this HTGW phenotype as a useful marker for the detection of subjects with high cardiometabolic risk in healthy Korean adults.

Association of low baseline free thyroxin levels with progression of coronary artery calcification over 4 years in euthyroid subjects: the Kangbuk Samsung Health Study

Overt and subclinical hypothyroidism are risk factors for atherosclerosis and cardiovascular diseases. It is unclear whether thyroid hormone levels within the normal range are also associated with atherosclerosis measured by coronary artery calcium (CAC).

Point‐Defect‐Passivated MoS2 Nanosheet‐Based High Performance Piezoelectric Nanogenerator

In this work, a sulfur (S) vacancy passivated monolayer MoS2 piezoelectric nanogenerator (PNG) is demonstrated, and its properties before and after S treatment are compared to investigate the effect of passivating S vacancy. The S vacancies are effectively passivated by using the S treatment process on the pristine MoS2 surface. The S vacancy site has a tendency to covalently bond with S functional groups; therefore, by capturing free electrons, a S atom will form a chemisorbed bond with the S vacancy site of MoS2 . S treatment reduces the charge-carrier density of the monolayer MoS2 surface, thus the screening effect of piezoelectric polarization charges by free carrier is significantly prevented. As a result, the output peak current and voltage of the S-treated monolayer MoS2 nanosheet PNG are increased by more than 3 times (100 pA) and 2 times (22 mV), respectively. Further, the S treatment increases the maximum power by almost 10 times. The results suggest that S treatment can reduce free-charge carrier by sulfur S passivation and efficiently prevent the screening effect. Thus, the piezoelectric output peaks of current, voltage, and maximum power are dramatically increased, as compared with the pristine MoS2 .