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Precursor designs for Cu<sub>2</sub>ZnSn(S,Se)<sub>4</sub> thin-film solar cells
Yang, Kee-Jeong,Sim, Jun-Hyoung,Son, Dae-Ho,Kim, Young-Ill,Kim, Dae-Hwan,Nam, Dahyun,Cheong, Hyeonsik,Kim, SeongYeon,Kim, JunHo,Kang, Jin-Kyu unknown 2017 Nano energy Vol.35 No.-
<P><B>Abstract</B></P> <P>To commercialize Cu<SUB>2</SUB>ZnSn(S,Se)<SUB>4</SUB> (CZTSSe) thin-film solar cells, it is necessary to improve their efficiency and to develop the technological ability to produce large-area modules. Defect formation due to the secondary phase is considered to be one of the main reasons for decreased CZTSSe thin-film solar-cell efficiency. This study explores the potential capabilities of large-area thin-film solar cells by controlling the defect formation using various CZTSSe precursor designs, and by improving the characteristic uniformity within the thin-film solar cells. Alloying the precursor as a stack of discrete layers can result in lateral segregation of elements into stable-phase islands, yielding a non-uniform composition on small length scales. It is found that the application of an indiscrete layer by minimizing the precursor-layer thickness allows avoiding Zn rich inhomogeneities in the absorber that would favor formation of detrimental ZnS-ZnSe secondary phases and deep defects. Among the various precursor layers designed by considering the reaction mechanism under annealing, a sample with 15 precursor layers is found to exhibit a shallow electron-acceptor energy level, high photovoltaic conversion efficiency, and uniform characteristics over the corresponding thin-film solar cell. Based on such improvements in both the efficiency and characteristic distribution, it is expected that the commercialization of CZTSSe thin-film solar cells can be advanced.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An indiscrete layer enabled the suppression of the overly rich Zn zone. </LI> <LI> It prevents the formation of Zn-rich detrimental secondary phases and defects. </LI> <LI> A sample with 15 precursor layers exhibits a shallow acceptor energy level. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>An indiscrete layer was chosen as a precursor stacking order design, which enabled the suppression of the overly rich Zn zone during a relatively low-temperature annealing process, thus preventing the formation of Zn-rich detrimental secondary phases and defects in these regions. A higher PCE and a uniform composition ratio distribution, which helped to realize uniform characteristics across the solar cell, were obtained.</P> <P>[DISPLAY OMISSION]</P>
Development of a CUBRID-Based Distributed Parallel Query Processing System
( Hyeong-il Kim ),( Hyeonsik Yang ),( Min Yoon ),( Jae-woo Chang ) 한국정보처리학회 2017 Journal of information processing systems Vol.13 No.3
Due to the rapid growth of the amount of data, research on bigdata processing has been highlighted. For bigdata processing, CUBRID Shard is able to support query processing in parallel way by dividing the database into a number of CUBRID servers. However, CUBRID Shard can answer a user`s query only when the query is required to gain accesses to a single CUBRID server, instead of multiple ones. To solve the problem, in this paper we propose a CUBRID based distributed parallel query processing system that can answer a user`s query in parallel and distributed manner. Finally, through the performance evaluation, we show that our proposed system provides 2-3 times better performance on query processing time than the existing CUBRID Shard.
Development of a CUBRID-Based Distributed Parallel Query Processing System
Kim, Hyeong-Il,Yang, HyeonSik,Yoon, Min,Chang, Jae-Woo Korea Information Processing Society 2017 Journal of information processing systems Vol.13 No.3
Due to the rapid growth of the amount of data, research on bigdata processing has been highlighted. For bigdata processing, CUBRID Shard is able to support query processing in parallel way by dividing the database into a number of CUBRID servers. However, CUBRID Shard can answer a user's query only when the query is required to gain accesses to a single CUBRID server, instead of multiple ones. To solve the problem, in this paper we propose a CUBRID based distributed parallel query processing system that can answer a user's query in parallel and distributed manner. Finally, through the performance evaluation, we show that our proposed system provides 2-3 times better performance on query processing time than the existing CUBRID Shard.
Nam, Dahyun,Cho, Soyeon,Sim, Jun-Hyoung,Yang, Kee-Jeong,Son, Dae-Ho,Kim, Dae-Hwan,Kang, Jin-Kyu,Kwon, Min-Su,Jeon, Chan-Wook,Cheong, Hyeonsik Elsevier 2016 Solar Energy Materials and Solar Cells Vol.149 No.-
<P><B>Abstract</B></P> <P>We found a clear correlation between the solar conversion efficiency and the distribution of the ZnS secondary phase in Cu<SUB>2</SUB>ZnSnS<SUB>4</SUB> (CZTS) solar cells. Five CZTS solar cells were prepared by the two-step process in which sputtered precursor multilayers were sulfurized at different temperatures. In higher efficiency solar cells, the ZnS secondary phase was found to accumulate near the interface between CZTS and MoS<SUB>2</SUB> formed on top of the Mo layer. It was also found that a solar cell with a higher efficiency showed weaker ZnS Raman signal in the MoS<SUB>2</SUB> layer. The highest conversion efficiency of 7.5% was obtained from a solar cell prepared at a sulfurization temperature of 570°C, in which no ZnS was detected in the MoS<SUB>2</SUB> layer. We suggest that in order to obtain a high efficiency CZTS solar cell, it is critical to find a condition that keeps ZnS from the MoS<SUB>2</SUB> layer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZnS in the MoS<SUB>2</SUB> layer of Cu<SUB>2</SUB>ZnSnS<SUB>4</SUB> solar cells reduces the efficiency. </LI> <LI> In a high efficiency cell, no ZnS was detected in the MoS<SUB>2</SUB> layer. </LI> <LI> ZnS tends to accumulate in the CZTS layer near the CZTS/MoS<SUB>2</SUB> interface. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>