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Dopant-Free All-Back-Contact Si Nanohole Solar Cells Using MoO<sub><i>x</i></sub> and LiF Films
Um, Han-Don,Kim, Namwoo,Lee, Kangmin,Hwang, Inchan,Seo, Ji Hoon,Seo, Kwanyong American Chemical Society 2016 Nano letters Vol.16 No.2
<P>We demonstrate novel all-back-contact Si nanohole solar cells via the simple direct deposition of molybdenum oxide (MoOx) 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 MoOx 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 MoOx/Si interface and suppressed recombitiation at the Si and LiF/Al electrode interface. With optimized MoOx and LiF film thickness as well as the all-back-contact design, our 1 cm(2) 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 (similar to 400 nm), resulting in a dramatic improvement (54.6%) in the short-circuit current density (36.8 mA/cm(2)) compared to that of a planar cell (23.8 mA/cm(2)). Hence, our all-back-contact design using MoOx and LiF films formed by a simple deposition process presents a unique opportunity to develop highly efficient and low-cost nanostructured Si solar cells.</P>
Embedded Metal Electrode for Organic–Inorganic Hybrid Nanowire Solar Cells
Um, Han-Don,Choi, Deokjae,Choi, Ahreum,Seo, Ji Hoon,Seo, Kwanyong American Chemical Society 2017 ACS NANO Vol.11 No.6
<P>We demonstrate here an embedded metal electrode for highly efficient organic inorganic hybrid nanowire solar cells. The electrode proposed here is an effective alternative to the conventional bus and finger electrode which leads to a localized short circuit at a direct Si/metal contact and has a poor collection efficiency due to a nonoptimized electrode design. In our design, a Ag/SiO2 electrode is embedded into a Si substrate while being positioned between Si nanowire arrays underneath poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), facilitating suppressed recombination at the Si/Ag interface and notable improvements in the fabrication reproducibility. With an optimized microgrid electrode, our 1 cm(2) hybrid solar cells exhibit a power conversion efficiency of up to 16.1% with an open-circuit voltage of 607 mV and a short circuit current density of 34.0 mA/cm(2). This power conversion efficiency is more than twice as high as that of solar cells using a conventional electrode (8.0%). The microgrid electrode significantly minimizes the optical and electrical losses. This reproducibly yields a superior quantum efficiency of 99% at the main solar spectrum wavelength of 600 nm. In particular, our solar cells exhibit a significant increase in the fill factor of 78.3% compared to that of a conventional electrode (61.4%); this is because of the drastic reduction in the metal/contact resistance of the 1 mu m-thick Ag electrode. Hence, the use of our embedded microgrid electrode in the construction of an ideal carrier collection path presents an opportunity in the development of highly efficient organic inorganic hybrid solar cells.</P>
Um, Han-Don,Park, Kwang-Tae,Jung, Jin-Young,Li, Xiaopeng,Zhou, Keya,Jee, Sang-Won,Lee, Jung-Ho RSC Pub 2014 Nanoscale Vol.6 No.10
<P>Formation of a selective emitter in crystalline silicon solar cells improves photovoltaic conversion efficiency by decoupling emitter regions for light absorption (moderately doped) and metallization (degenerately doped). However, use of a selective emitter in silicon nanowire (Si NW) solar cells is technologically challenging because of difficulties in forming robust Ohmic contacts that interface directly with the top-ends of nanowires. Here we describe a self-aligned selective emitter successfully integrated into an antireflective Si NW solar cell. By one-step metal-assisted chemical etching, NW arrays formed only at light-absorbing areas between top-metal grids while selectively retaining Ohmic contact regions underneath the metal grids. We observed a remarkable 40% enhancement in blue responses of internal quantum efficiency, corresponding to a conversion efficiency of 12.8% in comparison to the 8.05% of a conventional NW solar cell.</P>
Um, Han-Don,Choi, Keun-Ho,Hwang, Inchan,Kim, Se-Hee,Seo, Kwanyong,Lee, Sang-Young The Royal Society of Chemistry 2017 ENERGY AND ENVIRONMENTAL SCIENCE Vol.10 No.4
<P>The combination of energy generation and energy storage systems is the ultimate solution to meet the ever-increasing demand for high-energy-density power sources. Here, we demonstrate a new class of monolithically integrated, photo-rechargeable portable power sources based on miniaturized crystalline Si photovoltaics (c-Si PVs) and printed solid-state lithium-ion batteries (LIBs). A solid-state LIB with a bipolar cell configuration is fabricated directly on the aluminium electrode of a c-Si PV module through an in-series printing process, which enables the seamless architectural/electrical connection of the two different energy systems. The single-unit PV-LIB device shows exceptional electrochemical performance that lies far beyond those achievable by conventional PVs or LIBs alone: it displays fast, low-light-intensity and high-temperature photo-charging; a photo-electric conversion/storage efficiency of 7.61%; a sustainable cycling performance; and continuous discharging at an extremely high current density of 28C under sunlight illumination. This study opens a facile and scalable route for the development of single-unit, photo-rechargeable mobile high-performance batteries that are required for the future era of ubiquitous electronics.</P>
18.4%-Efficient Heterojunction Si Solar Cells Using Optimized ITO/Top Electrode
Kim, Namwoo,Um, Han-Don,Choi, Inwoo,Kim, Ka-Hyun,Seo, Kwanyong American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.18
<P>We optimize the thickness of a transparent conducting oxide (TCO) layer, and apply a microscale mesh pattern metal electrode for high-efficiency a-Si/c-Si heterojunction solar cells. A solar cell equipped with the proposed microgrid metal electrode demonstrates a high short-circuit current density (J(sc)) of 40.1 mA/cm(2), and achieves a high efficiency of 18.4% with an open-circuit voltage (V-OC) of 618 mV and a fill factor (FF) of 74.1% as result of the shortened carrier path length and the decreased electrode area of the microgrid metal electrode. Furthermore, by optimizing the process sequence for electrode formation, we are able to effectively restore the reduction in V-OC that occurs during the microgrid metal electrode formation process. This work is expected to become a fundamental study that can effectively improve current loss in a-Si/c-Si heterojunction solar cells through the optimization of transparent and metal electrodes.</P>
병원 건물의 히트펌프 냉난방 시스템 적용을 위한 시뮬레이션 연구
최영돈(Young Don Choi),한성호(Seong Ho Han),조성환(Sung Hwan Cho),김두성(Du Sung Kim),엄철준(Chul Jun Um) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.4
In Korea, air source heat pump system is less efficient than conventional heat source facilities, because the air temperature in winter season is so low that COP of air source heat pump system drops below 3.0. Therefore, the study on the application of heat pump heating and cooling systems is crucial for the efficient popularization of heat pump. In this work, we present the dynamic analysis of energy consumption for the large hospital building by heat resistance-capacitance method. The system simulation of water storage air source heat pump is additionally performed by changing sizes and locations of the hospital building. The computed results show that energy cost of water storage air source heat pump is low, so it is more economical than absorption chiller & heater.