Ji-won Lee

A polymer gel electrolyte to achieve ≥6% power conversion efficiency with a novel organic dye incorporating a low-band-gap chromophore

A quasi-solid-state dye-sensitized solar cell with novel organic sensitizers incorporating a benzothiadiazole chromophore showed excellent long-term stability, which exhibited 10% decrease during the 1000 h light soaking; the optimized cell gave a short circuit photocurrent density of 12.03 mA cm−2, an open circuit voltage of 0.720 V and a fill factor of 0.76, corresponding to an overall conversion efficiency of 6.61% under standard global AM 1.5 solar conditions.

Enhanced electron diffusion length of mesoporous TiO2 film by using Nb2O5 energy barrier for dye-sensitized solar cells

Electron diffusion coefficient (D) and electron lifetime (τ) of mesoporous TiO2 films with Nb2O5 energy barrier were investigated by the stepped light-induced transient measurements of photocurrent and photovoltage, compared with that without the Nb2O5. Both the D and τ values were significantly increased with the Nb2O5 energy barrier, resulting in remarkable enhancements of electron diffusion length and optimum thickness of the TiO2 film. As a result, the Nb2O5 energy barrier could provide much more efficient dye-sensitized solar cells by the additional effect of the improved optimum thickness as well as the existing effect at the same TiO2 film thickness.

Linkage of N3 dye to N3 dye on nanocrystalline TiO2 through trans-1,2-bis(4-pyridyl)ethylene for enhancement of photocurrent of dye-sensitized solar cells

Linking of N3 dye to another TiO2-attached N3 dye rendered an enhanced short-circuit photocurrent and thereby higher efficiency for the dye-sensitized solar cell with the pertinent TiO2 film electrode.

Influence of surface properties on the performance of Cu(In,Ga)(Se,S)2 thin-film solar cells using Kelvin probe force microscopy

We have investigated the sulfurization process in a Cu(In,Ga)(Se,S)2 (CIGSS) absorber layer fabricated by a two-step sputter and selenization/sulfurization method in order to make an ideal double-graded band-gap profile and increase the open circuit voltage (Voc). The sulfurization process was controlled by temperature from 570 °C to 590 °C without changing H2S gas concentration and reaction time. Although the energy band-gap of the CIGSS absorber layer was increased with increasing sulfurization temperature, the Voc of the completed CIGSS device fabricated at 590 °C sulfurization temperature did not increase. In order to investigate this abnormal Voc behavior, the CIGSS absorber layer was measured by local electrical characterization utilizing Kelvin probe force microscopy, especially in terms of grain boundary potential and surface work function. Consequently, the abnormal Voc behavior was attributed to the degradation of grain boundary passivation by the strong sulfurization process. The optimum sulfurization temperature plays an important role in enhancement of grain boundary passivation. It was also verified that the Voc degradation in the CIGSS solar cell fabricated by the two-step method is more influenced by the grain boundary passivation quality in comparison with the slight non-uniformity of material composition among grains.

Electrochemical sulphur dioxide oxidation with platinum-aluminum electrocatalysts

Platinum-aluminum electrocatalysts supported on carbon black were investigated for electrogenerative sulfur dioxide (SO2) oxidation in hybrid type, liquid-phase SO2/O2 cells. Incorporation of aluminum with platinum electrocatalysts on carbon resulted in an electrocatalytic activity increase for S02 oxidation over the whole investigated range (1–30 at % aluminum). Significant synergistic effect from aluminum was observed when even a small amount, as little as 1 at %, was incorporated in the platinum. A maximum 68 % improvement was obtained when 10 at % aluminum was incorporated in the platinum. Results of an ESCA study and electrochemical platinum surface area measurement supported the hypothesis of an electronic interaction between platinum and aluminum.

Enhancement in Performance of Dye-Sensitized Solar Cells Modified with In Situ Photopolymerized PDEA in TiO2 Films

Beneficial effects of in situ photopolymerized poly[di-(ethylene glycol)-2-ethyl hexyl ether acrylate] (PDEA) in the pores of dye-coated TiO 2 film on the photovoltaic characteristics of dye-sensitized solar cells (DSSCs)are reported. We have found remarkable enhancements of short-circuit photocurrent (J s c ) by 39% and of open-circuit voltage (V O C ) by 40 mV for the PDEA-modified DSSC compared with those of a conventional DSSC. This led to an enhancement in the overall solar energy conversion efficiency of 4.9% for the modified cell over 4.0% for a cell without PDEA at 100 mW/cm 2 . Moreover, the PDEA modification has led to improved long-term stability of the DSSC. Analyses of optical absorption and transient photocurrent of the cells suggest that the increased concentration of photo-injected electrons as a result of blocking of trap states in TiO 2 contributes to the enhancement in the J S C of PDEA-modified DSSCs. The V O C increase is attributed to an improved screening of the conduction band electrons from I 3 - ions in the presence of PDEA adhered to TiO 2 particles.

Consecutive CVD of Al ∕ Co Bilayers on SiO2 or Alq3 Surfaces at Low Temperature of 70 ° C

There are difficulties in the nucleation of Al on SiO 2 and polymer surfaces at temperatures below 100°C using MPA as the Al precursor. In this study, Al/Co bilayer structures were deposited on SiO 2 or tris-(8-hydroxyquinoline) aluminum (Alq 3 ) surfaces at a low temperature of 70°C using a consecutive chemical vapor deposition (CVD) method. The use of Co 2 (CO) 8 as a precursor allowed the deposition of a continuous Co thin film on SiO 2 at 70°C, which provided effective nucleation sites for Al CVD at the same temperature. The predeposited Co underlayer was used to promote the nucleation of Al using MPA as the Al precursor. This resulted in the deposition of uniformly thick Al thin films with a smooth surface morphology (root-mean-square = 7.3 nm for 110 nm thick Al), a low resistivity of 4.2 μΩ cm, and negligible carbon contamination. Compared with the continuous films of Co on SiO 2 , there is isolated growth of Co on Alq 3 surfaces, which resulted in Al thin films with a rough surface (root-mean-square = 83.2 nm for 70-140 nm Al), a resistivity of 3.4-7.5 μΩ cm, and 3.0 atom % C contamination.

Trends in the prevalence of type 2 diabetes and its association with mortality rates in Asians vs. Whites: Results from the United States National Health Interview Survey from 2000 to 2014

AIMS To identify the prevalence and mortality of type 2 diabetes in Asian Americans (Asians) vs. non-Hispanic whites (Whites). METHODS We analyzed a nationally representative sample of 237,354 U.S. adults aged ≥30 years using National Health Interview Survey data from 2000 to 2014 to estimate the prevalence and trends of type 2 diabetes. Additionally, 144,638 Asians and Whites represented in surveys from 2000 to 2009 were included in the mortality analysis with follow-up to 2011. RESULTS Type 2 diabetes was higher in Asians than Whites (7.0-11.2 vs. 5.6-8.3%) and increased over time. Prevalence rates increased from 8.1 (2000-2002) to 9.6% (2012-2014) in Asians and from 6.0 (2000-2002) to 7.9% (2012-2014) in Whites (both P < 0.05). The age-standardized mortality rates were 72.7 and 138.8 per 1000 person-years in Asians and Whites with diabetes, respectively, and 58.1 and 77.8 per 1000 person-years, respectively, in those without diabetes. Among Asians and Whites with diabetes, hazard ratios for total and CVD mortality were 0.7 (95% CI: 0.5-0.9) and 0.3 (95% CI: 0.1-0.6), respectively, with no difference in cancer mortality. Asians and Whites without diabetes exhibited no differences in total or cause-specific mortality. CONCLUSIONS Type 2 diabetes was more prevalent in Asians, with a significant upward trend since 2000, but overall mortality was lower in Asians than Whites with diabetes. Asians are susceptible to type 2 diabetes; thus, prevention programs are still needed.