• Current Photovoltaic Research
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• v.2 no.3
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• pp.103-109
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• 2014

Highly efficient hydrogenated nanocrystalline silicon (nc-Si:H) thin-film solar cells were prepared on flexible stainless steel substrates using plasma-enhanced chemical vapor deposition. To enhance the performance of solar cells, material properties of back reflectors, n-doped seed layers and wide bandgap nc-SiC:H window layers were optimized. The light scattering efficiency of Ag back reflectors was improved by increasing the surface roughness of the films deposited at elevated substrate temperatures. Using the n-doped seed layers with high crystallinity, the initial crystal growth of intrinsic nc-Si:H absorber layers was improved, resulting in the elimination of the defect-dense amorphous regions at the n/i interfaces. The nc-SiC:H window layers with high bandgap over 2.2 eV were deposited under high hydrogen dilution conditions. The vertical current flow of the films was enhanced by the formation of Si nanocrystallites in the amorphous SiC:H matrix. Under optimized conditions, a high conversion efficiency of 9.13% ($V_{oc}=0.52$, $J_{sc}=25.45mA/cm^2$, FF = 0.69) was achieved for the flexible nc-Si:H thin-film solar cells.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.64.2-64.2
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• 2011

a-Si 박막 태양전지는 a-Si:H을 유리 기판 사이에 주입해 만드는 태양전지로, 뛰어난 적용성과 경제성을 지녔으나 c-Si 태양전지에 비해 낮은 변환 효율을 보이는 단점이 있다. 변환 효율을 높이기 위한 연구 방법으로는 a-Si 박막 태양전지 단일cell 제작 시 high Bandgap을 가지는 p-layer를 사용함으로 높은 Voc와 Jsc의 향상에 기여할 수 있는데, 이 때 p-layer의 defect 증가와 activation energy 증가도 동시에 일어나 변환 효율의 증가폭을 감소시킨다. 이를 보완하기 위해 본 실험에서는 p-layer에 기존의 p-a-Si:H를 사용함과 동시에 high Bandgap의 buffer layer를 p-layer와 i-layer 사이에 삽입함으로써 그 장점을 유지하고 높은 defect과 낮은 activation energy의 영향을 최소화하였다. ASA 시뮬레이션을 통해 a-Si:H보다 high Bandgap을 가지는 a-SiOx 박막을 사용하여 p-type buffer layer의 두께를 2nm, Bandgap 2.0eV, activation energy를 0.55eV로 설정하고, i-type buffer layer의 두께를 2nm, Bandgap 1.8eV로 설정하여 삽입하였을 때 박막 태양전지의 변환 효율 10.74%를 달성할 수 있었다. (Voc=904mV, Jsc=$17.48mA/cm^2$, FF=67.97).

• Solar Energy
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• v.10 no.3
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• pp.46-52
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• 1990

Novel a-Si solar cells with delta-doped(${\delta}x$-doped) P-layer have been fabricated to enhance the hole concentration of the P-layers. The ${\delta}-$doped P-layer consists of very thin B sheets of 0.1-0.5 atomic layers and undoped a-SiC multi-layers. B-layers were prepared by photo-CVD and pyrolysis technique. The structural, optical and electrical characteristics of the delta-doped P-layer films were evaluated by means of FTIR, AES and SIMS. As the results of this study, it was found that the ${\delta}$-doped P-layer showed much superior optical and electrical characteristics than those of conventional uniformly B-doped a-Si layers. 12.5% energy conversion efficiency was achieved for the Cell with ${\delta}$-doped P-layer.

• Journal of the Korean Ceramic Society
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• v.51 no.3
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• pp.197-200
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• 2014

We investigated the influence of blistering on $Al_2O_3$/SiON stacks and $Al_2O_3$/SiNx:H stacks passivation layers. $Al_2O_3$ film provides outstanding Si surface passivation quality. $Al_2O_3$ film as the rear passivation layer of a p-type Si solar cell is usually stacked with a capping layer, such as $SiO_2$, SiNx, and SiON films. These capping layers protect the thin $Al_2O_3$ layer from an Al electrode during the annealing process. We compared $Al_2O_3$/SiON stacks and $Al_2O_3$/SiNx:H stacks through surface morphology and minority carrier lifetime after annealing processes at $450^{\circ}C$ and $850^{\circ}C$. As a result, the $Al_2O_3$/SiON stacks were observed to produce less blister phenomenon than $Al_2O_3$/SiNx:H stacks. This can be explained by the differences in the H species content. In the process of depositing SiNx film, the rich H species in $NH_3$ source are diffused to the $Al_2O_3$ film. On the other hand, less hydrogen diffusion occurs in SiON film as it contains less H species than SiNx film. This blister phenomenon leads to an increase insurface defect density. Consequently, the $Al_2O_3$/SiON stacks had a higher minority carrier lifetime than the $Al_2O_3$/SiNx:H stacks.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.230-234
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• 2009

It is significant technique to increase competitiveness that solar cells have a high energy conversion efficiency and cost effectiveness. When making high efficiency crystalline Si solar cells, evaporated Ti/Pd/Ag contact system is widely used in order to reduce the electrical resistance of the contact fingers. However, the evaporation process is no applicable to mass production because high vacuum is needed. Furthermore, those metals are too expensive to be applied for terrestrial applications. Ni/Cu/Ag contact system of silicon solar cells offers a relatively inexpensive method of making electrical contact. Ni silicide formation is one of the indispensable techniques for Ni/Cu/Ag contact sytem. Ni was electroless plated on the front grid pattern, After Ni electroless plating, the cells were annealed by RTP(Rapid Thermal Process). Ni silicide(NiSi) has certain advantages over Ti silicide($TiSi_2$), lower temperature anneal, one step anneal, low resistivity, low silicon consumption, low film stress, absence of reaction between the annealing ambient. Ni/Cu/Ag metallization scheme is an important process in the direction of cost reduction for solar cells of high efficiency. In this article we shall report an investigation of rapid thermal silicidation of nickel on silngle crystalline silicon wafers in the annealing range of $350-390^{\circ}C$. The samples annealed at temperatures from 350 to $390^{\circ}C$ have been analyzed by SEM(Scanning Electron Microscopy).

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.586-591
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• 2010

Solar cells have been more intensely studied as part of the effort to find alternatives to fossil fuels as power sources. The progression of the first two generations of solar cells has seen a sacrifice of higher efficiency for more economic use of materials. The use of a single junction makes both these types of cells lose power in two major ways: by the non-absorption of incident light of energy below the band gap; and by the dissipation by heat loss of light energy in excess of the band gap. Therefore, multi junction solar cells have been proposed as a solution to this problem. However, the $1^{st}$ and $2^{nd}$ generation solar cells have efficiency limits because a photon makes just one electron-hole pair. Fabrication of all-silicon tandem cells using an Si quantum dot superlattice structure (QD SLS) is one possible suggestion. In this study, an $SiO_x$ matrix system was investigated and analyzed for potential use as an all-silicon multi-junction solar cell. Si quantum dots with a super lattice structure (Si QD SLS) were prepared by alternating deposition of Si rich oxide (SRO; $SiO_x$ (x = 0.8, 1.12)) and $SiO_2$ layers using RF magnetron co-sputtering and subsequent annealing at temperatures between 800 and $1,100^{\circ}C$ under nitrogen ambient. Annealing temperatures and times affected the formation of Si QDs in the SRO film. Fourier transform infrared spectroscopy (FTIR) spectra and x-ray photoelectron spectroscopy (XPS) revealed that nanocrystalline Si QDs started to precipitate after annealing at $1,100^{\circ}C$ for one hour. Transmission electron microscopy (TEM) images clearly showed SRO/$SiO_2$ SLS and Si QDs formation in each 4, 6, and 8 nm SRO layer after annealing at $1,100^{\circ}C$ for two hours. The systematic investigation of precipitation behavior of Si QDs in $SiO_2$ matrices is presented.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.378-381
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• 2008

고효율 a-Si:H/c-Si 이종접합 태양전지를 얻기 위해서는 우수한 c-Si wafer 위에 고품질의 비정질 실리콘박막을 통한 heterointerface를 형성하는 것이 매우 중요하다. 이를 달성하기 위해서는 공정중에 오염되기 쉬운 Si wafer 표면 상태를 정확히 검사하고 잘 관리하여야 한다. 본 연구에서는 세정 및 표면산화에 따른 Si wafer 상태를 Spectroscopic Ellipsometry 및 u-PCD를 이용하여 분석하였으며, <$\varepsilon$2> @4.25eV 값이 Si wafer 상태를 잘 나타내고 있음을 확인하였고 세정 최적화 할 경우 그 값이 43.02에 도달하였다. 또한 RF-PECVD로 증착된a-Si:H 박막을 EMA 모델링을 통해 분석한 결과 낮은 결정성과 높은 밀도를 가지는 a-Si:H를 얻을 수 있었으며, 이를 이종접합 태양전지에 적용한 결과 Flat wafer상에서 10.88%, textured wafer 적용하여 13.23%의 변환효율을 얻었다. 결론적으로 Spectroscopic Ellipsometry가 매우 얇고 고품질의 다층 박막이 필요한 이종접합 태양전지 분석에 있어 매우 유용한 방법임이 확인되었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.193-193
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• 2012

In thin film silicon solar cells, p-i-n structure is adopted instead of p/n junction structure as in wafer-based Si solar cells. PECVD is the most widely used thin film deposition process for a-Si:H or ${\mu}c$-Si:H solar cells. Single-chamber PECVD system for a-Si:H solar cell manufacturing has the advantage of lower initial investment and maintenance cost for the equipment. However, in single-chamber PECVD system, doped and intrinsic layers are deposited in one plasma chamber, which inevitably impedes sharp dopant profiles at the interfaces due to the contamination from previous deposition process. The cross-contamination between layers is a serious drawback of single-chamber PECVD system. In this study, a new plasma process to solve the cross-contamination problem in a single-chamber PECVD system was suggested. In order to remove the deposited B inside of the plasma chamber during p-layer deposition, a high RF power was applied right after p-layer deposition with SiH4 gas off, which is then followed by i-layer, n-layer, and Ag top-electrode deposition without vacuum break. In addition to the p-i interface control, various interface control techniques such as FTO-glass pre-annealing in O2 environment to further reduce sheet resistance of FTO-glass, thin layer of TiO2 deposition to prevent H2 plasma reduction of FTO layer, and hydrogen plasma treatment prior to n-layer deposition, etc. were developed. The best initial solar cell efficiency using single-chamber PECVD system of 10.5% for test cell area of 0.2 $cm^2$ could be achieved by adopting various interface control methods.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.148-148
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• 2011

Recently, there have been many research activities to develop the large-area plasma source, which is able to generate the high-density plasma with relatively good uniformity, for the plasma processing in the thin-film solar cell and display panel industries. The large-area CCP sources have been applied to the PECVD process as well as the etching. Especially, the PECVD processes for the depositions of various films such as a-Si:H, ${\mu}c$-Si:H, Si3N4, and SiO2 take a significant portion of processes. In order to achieve higher deposition rate (DR), good uniformity in large-area reactor, and good film quality (low defect density, high film strength, etc.), the application of VHF (>40 MHz) CCP is indispensible. However, the electromagnetic wave effect in the VHF CCP becomes an issue to resolve for the achievement of good uniformity of plasma and film. Here, we propose a new electrode as part of a method to resolve the standing wave effect in the large-area VHF CCP. The electrode is split up a series of strip-type electrodes and the strip-type electrodes and the ground ones are arranged by turns. The standing wave effect in the longitudinal direction of the strip-type electrode is reduced by using the multi-feeding method of VHF power and the uniformity in the transverse direction of the electrodes is achieved by controlling the gas flow and the gap length between the powered electrodes and the substrate. Also, we provide the process results for the growths of the a-Si:H and the ${\mu}c$-Si:H films. The high DR (2.4 nm/s for a-Si:H film and 1.5 nm/s for the ${\mu}c$-Si:H film), the controllable crystallinity (~70%) for the ${\mu}c$-Si:H film, and the relatively good uniformity (1% for a-Si:H film and 7% for the ${\mu}c$-Si:H film) can be obtained at the high frequency of 40 MHz in the large-area discharge (280 mm${\times}$540 mm). Finally, we will discuss the issues in expanding the multi-electrode to the 8G class large-area plasma processing (2.2 m${\times}$2.4 m) and in improving the process efficiency.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.3
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• pp.233-240
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• 2023

p-type Tunnel Oxide Passivating Contacts (TOPCon) solar cell is fabricated with a poly-Si/SiO_x structure. It simultaneously achieves surface passivation and enhances the carriers' selective collection, which is a promising technology for conventional solar cells. The quality of passivation is depended on the quality of the tunnel oxide layer at the interface with the c-Si wafer, which is affected by the bond of SiO formed during the subsequent annealing process. The highest cell efficiency reported to date for the laboratory scale has increased to 26.1%, fabricated by the Institute for Solar Energy Research. The cells used a p-type float zone silicon with an interdigitated back contact (IBC) structure that fabricates poly-Si and SiO_x layer achieves the highest implied open-circuit voltage (iV_oc) is 750 mV, and the highest level of edge passivation is 40%. This review presents an overview of p-type TOPCon technologies, including the ultra-thin silicon oxide layer (SiO_x) and poly-silicon layer (poly-Si), as well as the advancement of the SiO_x and poly-Si layers. Subsequently, the limitations of improving efficiency are discussed in detail. Consequently, it is expected to provide a basis for the simplification of industrial mass production.