Dopant-Free All-Back-Contact Si Nanohole Solar Cells Using MoO_<i>x</i> and LiF Films

We demonstrate novel all-back-contact Si nanohole solar cells via the simple direct deposition of molybdenum oxide (MoO_<i>x</i>) and lithium fluoride (LiF) thin films as dopant-free and selective carrier contacts (SCCs). This approach is in contrast to conventionally used high-temperature thermal doping processes, which require multistep patterning processes to produce diffusion masks. Both MoO_<i>x</i> and LiF thin films are inserted between the Si absorber and Al electrodes interdigitatedly at the rear cell surfaces, facilitating effective carrier collection at the MoO_<i>x</i>/Si interface and suppressed recombination at the Si and LiF/Al electrode interface. With optimized MoO_<i>x</i> and LiF film thickness as well as the all-back-contact design, our 1 cm² Si nanohole solar cells exhibit a power conversion efficiency of up to 15.4%, with an open-circuit voltage of 561 mV and a fill factor of 74.6%. In particular, because of the significant reduction in Auger/surface recombination as well as the excellent Si-nanohole light absorption, our solar cells exhibit an external quantum efficiency of 83.4% for short-wavelength light (∼400 nm), resulting in a dramatic improvement (54.6%) in the short-circuit current density (36.8 mA/cm²) compared to that of a planar cell (23.8 mA/cm²). Hence, our all-back-contact design using MoO_<i>x</i> and LiF films formed by a simple deposition process presents a unique opportunity to develop highly efficient and low-cost nanostructured Si solar cells

Differences in Pandemic-Related Factors Associated with Alcohol and Substance Use among Korean Adolescents: Nationwide Representative Study

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National trends in alcohol and substance use among adolescents from 2005 to 2021: a Korean serial cross-sectional study of one million adolescents

Background Although previous studies have provided data on early pandemic periods of alcohol and substance use in adolescents, more adequate studies are needed to predict the trends of alcohol and substance use during recent periods, including the mid-pandemic period. This study investigated the changes in alcohol and substance use, except tobacco use, throughout the pre-, early-, and mid-pandemic periods in adolescents using a nationwide serial cross-sectional survey from South Korea. Methods Data on 1,109,776 Korean adolescents aged 13–18 years from 2005 to 2021 were obtained in a survey operated by the Korea Disease Control and Prevention Agency. We evaluated adolescents’ alcohol and substance consumption prevalence and compared the slope of alcohol and substance prevalence before and during the COVID-19 pandemic to see the trend changes. We define the pre-COVID-19 period as consisting of four groups of consecutive years (2005–2008, 2009–2012, 2013–2015, and 2016–2019). The COVID-19 pandemic period is composed of 2020 (early-pandemic era) and 2021 (mid-pandemic era). Results More than a million adolescents successfully met the inclusion criteria. The weighted prevalence of current alcohol use was 26.8% [95% confidence interval (CI) 26.4–27.1] from 2005 to 2008 and 10.5% (95% CI 10.1–11.0) in 2020 and 2021. The weighted prevalence of substance use was 1.1% (95% CI 1.1–1.2) from 2005 to 2008 and 0.7% (95% CI 0.6–0.7) between 2020 and 2021. From 2005 to 2021, the overall trend of use of both alcohol and drugs was found to decrease, but the decline has slowed since COVID-19 epidemic (current alcohol use: βdiff 0.167; 95% CI 0.150–0.184; substance use: βdiff 0.152; 95% CI 0.110–0.194). The changes in the slope of current alcohol and substance use showed a consistent slowdown with regard to sex, grade, residence area, and smoking status from 2005 to 2021. Conclusion The overall prevalence of alcohol consumption and substance use among over one million Korean adolescents from the early and mid-stage (2020–2021) of the COVID-19 pandemic showed a slower decline than expected given the increase during the prepandemic period (2005–2019)

Estimated prevalence and trends in smoking among adolescents in South Korea, 2005–2021: a nationwide serial study

Background: Although smoking is classified as a risk factor for severe COVID-19 outcomes, there is a scarcity of studies on prevalence of smoking during the COVID-19 pandemic. Thus, this study aims to analyze the trends of prevalence of smoking in adolescents over the COVID-19 pandemic period. Methods: The present study used data from middle to high school adolescents between 2005 and 2021 who participated in the Korea Youth Risk Behavior Web-based Survey (KYRBS). We evaluated the smoking prevalence (ever or daily) by year groups and estimated the slope in smoking prevalence before and during the pandemic. Results: A total of 1,137,823 adolescents participated in the study [mean age, 15.04 years [95% confidence interval (CI) 15.03–15.06]; and male, 52.4% (95% CI 51.7–53.1)]. The prevalence of ever smokers was 27.7% (95% CI 27.3–28.1) between 2005 and 2008 but decreased to 9.8% (95% CI 9.3–10.3) in 2021. A consistent trend was found in daily smokers, as the estimates decreased from 5.4% (95% CI 5.2–5.6) between 2005 and 2008 to 2.3% (95% CI 2.1–2.5) in 2021. However, the downward slope in the overall prevalence of ever smokers and daily smokers became less pronounced in the COVID-19 pandemic period than in the pre-pandemic period. In the subgroup with substance use, the decreasing slope in daily smokers was significantly more pronounced during the pandemic than during the pre-pandemic period. Conclusions: The proportion of ever smokers and daily smokers showed a less pronounced decreasing trend during the pandemic. The findings of our study provide an overall understanding of the pandemic’s impact on smoking prevalence in adolescents. [MediaObject not available: see fulltext.