• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.387-390
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• 2002

This paper presents deposition and characterizations of microcrystalline silicon(${\mu}$c-Si:H) films prepared by hot wire chemical vapor deposition at substrate temperature below 300$^{\circ}C$. The SiH$_4$ concentration[F(SiH$_4$)/F(SiH$_4$).+(H$_2$)] is critical parameter for the formation of Si films with microcrystalline phase. At 6% of silane concentration, deposited intrinsic ${\mu}$c-Si:H films shows sufficiently low dark conductivity and high photo sensitivity for solar cell applications. P-type ${\mu}$c-S:H films deposited by Hot-Wire CVD also shows good electrical properties by varying the rate of B$_2$H$\_$6/ to SiH$_4$ gas. The solar cells with structure of Al/nip ${\mu}$c-Si:H/TCO/g1ass was fabricated with single chamber Hot-Wire CVD. About 3% solar efficiency was obtained and applicability of HWCVD for thin film solar cells was proven in this research.

• Journal of the Korean Vacuum Society
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• v.16 no.3
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• pp.161-166
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• 2007

Photovoltaic (PV) technology permits the transformation of solar light directly into electricity. For the last five years, the photovoltaic sector has experienced one of the highest growth rates worldwide (over 30% in 2006) and for the next 20 years, the average production growth rate is estimated to be between 27% and 34% annually. Currently the cost of electricity produced using photovoltaic technology is above that for traditional energy sources, but this is expected to fall with technological progress and more efficient production processes. A large scale production of solar grade silicon material of high purity could supply the world demand at a reasonably lower cost. A shift from crystalline silicon to thin film is expected in the future. The technical limit for the conversion efficiency is about 30%. It is assumed that in 2030 thin films will have a major market share (90%) and the share of crystalline cells will have decreased to 10%. Our research at Sungkyunkwan University of South Korea is confined to crystalline silicon solar cell technology. We aim to develop a technology for low cost production of high efficiency silicon solar cell. We have successfully fabricated silicon solar cells of efficiency more than 16% starting with multicrystalline wafers and that of efficiency more than 17% on single crystalline wafers with screen printing metallization. The process of transformation from the first generation to second generation solar cell should be geared up with the entry of new approaches but still silicon seems to remain as the major material for solar cells for many years to come. Local barriers to the implementation of this technology may also keep continuing up to year 2010 and by that time the cost of the solar cell generated power is expected to be 60 cent per watt. Photovoltaic source could establish itself as a clean and sustainable energy alternate to the ever depleting and polluting non-renewable energy resource.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.211-211
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• 2012

The electrical loss of the photo-generated carriers is dominated by the recombination at the metal- semiconductor interface. In order to enhance the performance of the solar cells, many studies have been performed on the surface treatment with passivation layer like SiN, SiO2, Al2O3, and a-Si:H. In this work, Al2O3 thin films were investigated to reduce recombination at surface. The Al2O3 thin films have two advantages, such as good passivation properties and back surface field (BSF) effect at rear surface. It is usually deposited by atomic layer deposition (ALD) technique. However, ALD process is a very expensive process and it has rather low deposition rate. In this study, the ICP-assisted reactive magnetron sputtering method was used to deposit Al2O3 thin films. For optimization of the properties of the Al2O3 thin film, various fabrication conditions were controlled, such as ICP RF power, substrate bias voltage and deposition temperature, and argon to oxygen ratio. Chemical states and atomic concentration ratio were analyzed by x-ray photoelectron spectroscopy (XPS). In order to investigate the electrical properties, Al/(Al2O3 or SiO2,/Al2O3)/Si (MIS) devices were fabricated and characterized using the C-V measurement technique (HP 4284A). The detailed characteristics of the Al2O3 passivation thin films manufactured by ICP-assisted reactive magnetron sputtering technique will be shown and discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.10
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• pp.754-759
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• 2013

Aluminum oxide($Al_2O_3$) film deposited by atomic layer deposition (ALD) is known to supply excellent surface passivation properties on crystalline Si surfaces. Since $Al_2O_3$ has fixed negative charge, it forms effective surface passivation by field effect passivation on the rear side in p-type silicon solar cell. However, $Al_2O_3$ layer formed by ALD process needs very long process time, which is not applicable in mass production of silicon solar cells. In this paper, plasma-assisted ALD(PA-ALD) was applied to form $Al_2O_3$ to reduce the process time. $Al_2O_3$ synthesized by ALD on c-Si (100) wafers contains a very thin interfacial $SiO_2$ layer, which was confirmed by FTIR and TEM. To improve passivation quality of $Al_2O_3$ layer, the deposition temperature was changed in range of $150{\sim}350^{\circ}C$, then the annealing temperature and time were varied. As a result, the silicon wafer with aluminum oxide film formed in $250^{\circ}C$, $400^{\circ}C$ and 10 min for the deposition temperature, the annealing temperature and time, respectively, showed the best lifetime of 1.6ms. We also observed blistering with nanometer size during firing of $Al_2O_3$ deposited on p-type silicon.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1598-1600
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• 2003

Microcrystalline silicon(c-Si:H) thin-film solar cells are prepared with intrinsic Si-layer by hot wire CVD. The operating parameters of solar cells are strongly affected by the filament temperature ($T_f$) during intrinsic layer. Jsc and efficiency abruptly decreases with elevated $T_f$ to $1400^{\circ}C$. This deterioration of solar cell parameters are resulted from increase of crystalline volume fraction and corresponding defect density at high $T_f$ The heater temperature ($T_h$) are also critical parameter that controls device operations. Solar cells prepared at low $T_h$ (<$200^{\circ}C$) shows a similar operating properties with devices prepared at high $T_f$, i.e. low Jsc, Voc and efficiency. The origins for this result, however, are different with that of inferior device performances at high $T_f$. In addition the phase transition of the silicon films occurs at different silane concentration (SC) by varying filament temperature, by which highest efficiency with SC vanes with $T_f$.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.67.1-67.1
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• 2010

Triple junction solar cell을 위한 a-SiGe middle cell의 조건별 광학적 특성에 관한 연구를 실시하였다. a-SiGe I층은 GeH4 유량, 압력, H2 dilution ratio를 변화시켜 제조하였으며 전기적, 광학적 특성을 비교하여 최종적으로 선택된 조건을 triple junction solar cell에 적용하였다. a-SiGe I층은 Ge contents가 증가함에 따라 band gap은 감소하고 45% 이상의 조건에서는 700nm 전후 파장의 투과율이 감소하며, 압력이 감소함에 따라 band gap은 소폭 감소하나 700nm 전후 파장의 투과율은 증가하였다. 그리고 H2 ratio가 증가함에 따라 band gap은 소폭 감소하나 투과율에는 큰 변화가 없었다. 상기 결과를 바탕으로 최종적으로 선택된 조건에서 triple-junction solar cell을 제작하여 평가한 결과 초기 변환효율 9%의 결과를 얻었다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.56.1-56.1
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• 2010

결정질 실리콘 태양전지의 표면 ARC(Anti-reflection Coating)layer는 반사도를 줄여 광 흡수율을 증가시키고, passivation 효과를 통하여 표면 재결합을 감소 시켜 태양전지의 효율을 높이는 중요한 역할을 한다. Silicon nitride 박막은 외부 stress 요인에 대해 안정성을 담보할 수 있어야한다. 따라서, 본 연구에서는 굴절률 가변에 따른 silicon nitride 박막을 PECVD를 이용하여 증착하고, 항온/항습 stability test를 통해 박막의 안정성을 확인하였다. Silicon nitride 증착을 위해 PECVD를 이용하였고, 공정압력 0.8Torr, 증착온도 $450^{\circ}C$, 증착파워 300W에서 실험을 진행하였다 박막의 굴절률은 1.9~2.3의 범위로 가변하였다. 항온/항습에 대한 신뢰성을 test 하기 위하여 5시간동안의 test를 1cycle로 하여 20회 동안 실험을 실시하였다. 증착된 silicon nitride 박막의 lifetime은 firing 이후 57.8us로 가장 높았으며, 항온/항습 test 이후에도 유사한 경향을 확인 할 수 있었다. 또한, 100h 동안의 항온/항습 test 결과 silicon nitride 박막의 lifetme 감소는 8.5%에 불과했다. 본 연구를 통하여 온도와 습도의 변화에 따른 결정질 실리콘 태양전지의 SiNx 박막의 증착 공정 조건에 대한 신뢰성을 확인 할 수 있었다.

• Transactions on Electrical and Electronic Materials
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• v.18 no.2
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• pp.70-73
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• 2017

We investigated n-i-p type single junction hydrogenated amorphous silicon oxide solar cells. These cells were without front surface texture or back reflector. Maximum power point efficiency of these cells showed that an optimized device structure is needed to get the best device output. This depends on the thickness and defect density ($N_d$) of the active layer. A typical 10% photovoltaic device conversion efficiency was obtained with a $N_d=8.86{\times}10^{15}cm^{-3}$ defect density and 630 nm active layer thickness. Our investigation suggests a correlation between defect density and active layer thickness to device efficiency. We found that amorphous silicon solar cell efficiency can be improved to well above 10%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05b
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• pp.66-69
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• 2002

This paper presents deposition and characterizations of microcrystalline silicon$({\mu}c-Si:H)$ films prepared by hot wire chemical vapor deposition at substrate temperature below $300^{\circ}C$. The $SiH_{4}$ concentration$[F(SiH_{4})/F(SiH_{4})+F(H_{2})]$ is critical parameter for the formation of Si films with microcrystalline phase. At 6% of silane concentration, deposited intrinsic ${\mu}c-Si:H$ films shows sufficiently low dark conductivity and high photo sensitivity for solar cell applications. P-type ${\mu}c-Si:H$ films deposited by Hot-Wire CVD also shows good electrical properties by varying the rate of $B_{2}H_{6}$ to $SiH_{4}$ gas. The solar cells with structure of Al/nip ${\mu}c-Si:H$/TCO/glass was fabricated with single chamber Hot-Wire CVD. About 3% solar efficiency was obtained and applicability of HWCVD for thin film solar cells was proven in this research.

• 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.