• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.36.1-36.1
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• 2010

While the substrate-type solar cells with Cu(In,Ga)Se2 absorbers yield conversion efficiencies of up 20%[1], the highest published efficiency of Cu(In,Ga)Se2 superstrate solar cell is only 12.8% [2]. The commerciallized Cu(In,Ga)Se2 solar cells are made in the substrate configuration having the stacking sequence of substrate (soda lime glass)/back contact (molybdenum)/absorber layer (Cu(In,Ga)Se2)/buffer layer (cadmium sulfide)/window layer (transparent conductive oxide)/anti reflection layer (MgF2) /grid contact. Thus, it is not possible to illuminate the substrate-type cell through the glass substrate. Rather, it is necessary to illuminate from the opposite side which requires an elaborate transparent encapsulation. In contrast to that, the configuration of superstrate solar cell allows the illumination through the glass substrate. This saves the expensive transparent encapsulation. Usually, the high quality Cu(In,Ga)Se2 absorber requires a high deposition temperature over 550C. Therefore, the front contact should be thermally stable in the temperature range to realize a successful superstrate-type solar cell. In this study, it was tried to make a decent superstrate-type solar cell with the thermally stable ZnO:Al layer obtained by adjusting its deposition parameters in magnetron sputtering process. The effect of deposition condition of the layer on the cell performance will be discussed together with hall measurement results and current-voltage characteristics of the cells.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.83.1-83.1
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• 2010

Hydrogenated a-SiGe middle cell for triple junction solar cell was investigated with various process parameters. a-SiGe I-layer was deposited at substrate temperature $245^{\circ}C$ and hydrogen content(R) was up to 26.7. Low optical bandgap(1.45eV) of a-SiGe cell was applied for middle cell although a-SiGe single cell efficiency with low Ge content was higher. And this cell was applied to the middle cell of a glass superstrate type a-Si/a-SiGe/uc-Si triple junction solar cell. The triple junction solar cell was resulted in the initial efficiency of about 9%, area $0.25cm^2$, under global AM 1.5 illumination.

• Proceedings of the Materials Research Society of Korea Conference
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• 1998.05a
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• pp.98-98
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• 1998

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.464.2-464.2
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• 2014

태양 에너지는 미래 에너지원으로 각광받고 있는 중요한 에너지원이다. 다양한 태양전지 중 CuInS2(CIS) 박막형 태양전지는 높은 광흡수율과 조절가능한 밴드갭에너지를 가지고 있으며, 높은 장기 안정성과 광변환효율 등으로 많은 관심을 받고 있다. 최근 20.3%에 달하는 높은 광변환효율이 보고된 바 있으나, 이는 고진공 장비를 요구함으로 인해 초기 투자비용이 늘어남과 동시에 대량생산 측면에서 한계점이 지적되고 있다. 본 연구는 CIS계 태양전지를 보다 저온, 상압에서 제조하기 위해 Cu, In, S 전구체를 용매에 녹여 전구체 용액을 제조하였다. 이를 스핀코팅을 이용하여 CdS 버퍼층이 증착된 ZnO 나노구조에 코팅 후, 건조 및 열처리하여 광흡수층 박막을 증착하는 방법을 개발하였다. 본 연구에서는 superstrate 형태의 태양전지 구조를 이용하기 위하여window 층으로 쓰이는 ZnO 박막을 수열합성법을 통해 나노구조화하였다. 이를 통해 CIS 흡수층과의 접촉면적 증가에 따른 빛 흡수효율 증가 및 전하 이동 효과를 증가시킬 수 있었다. 각각의 나노구조의 SEM, XRD, UV-transmittance 분석을 통하여 살펴 보았으며, 결과적으로 상온, 상압에서 증착이 가능한 용액 공정을 통해 superstrate방식의 CIS 태양전지를 만들 수 있었다. 소면적 태양전지 제작을 통해 박막 구조에 비해 향상된 광변환 효율을 얻었다.

• New & Renewable Energy
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• v.2 no.3
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• pp.31-36
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• 2006

Superstrate pin amorphous silicon thin-film(a-Si:H) solar cells are prepared on $SnO_2:F$ and ZnO:Al transparent conducting oxides(TCO) in order to see the effect of TCO/p-layers on a-Si:H solar cell operation. The solar cells prepared on textured ZnO:Al have higher open circuit voltage VOC than cells prepared on $SnO_2:F$. Presence of thin microcrystalline p-type silicon layer(${\mu}c-Si:H$) between ZnO:Al and p a-SiC:H plays a major role by causing improvement in fill factor as well as $V_{OC}$ of a-Si:H solar cells prepared on ZnO:Al TCO. Without any treatment of pi interface, we could obtain high $V_{OC}$ of 994mV while keeping fill factor(72.7%) and short circuit current density $J_{SC}$ at the same level as for the cells on $SnO_2:F$ TCO. This high $V_{OC}$ value can be attributed to modification in the current transport in this region due to creation of a potential barrier.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.158-161
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• 2006

Superstrate pin amorphous silicon thin-film (a-Si:H) solar cells are prepared on $SnO_2:F$ and ZnO:Al transparent conducting oxides (TCO) In order to see the effect of TCO/P-layers on a-Si:H solar cell operation. The solar cells prepared on textured ZnO:Al have higher open circuit voltage $V_{oc}$ than cells prepared on $SnO_2:F$. Presence of thin microcrystalline p-type silicon layer $({\mu}c-Si:H)$ between ZnO:Al and p a-SiC:H plays a major role by causing improvement in fill factor as well as $V_{oc}$, of a-Si:H solar cells prepared on ZnO:Al TCO. Without any treatment of pi interface, we could obtain high $V_{oc}$, of 994mv while keeping fill factor (72.7%) and short circuit current density $J_{sc}$ at the same level as for the cells on $SnO_2:F$ TCO. This high $V_{oc}$ value can be attributed to modification in the current transport in this region due to creation of a potential barrier.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.46.2-46.2
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• 2010

For use of superstrate thin-film solar cells, surface texture of the transparent conductive oxide (TCO) has been used to enhance short-circuit currents by increasing light trapping into the cell. ZnO:Al films were deposited by using DC magnetron sputtering on glass substrates with ceramic (ZnO:$Al_2O_3$) target. The as-deposited TCO before texturing exhibited high transparencies (T > 85% for visible light including all reflection losses) and excellent electrical properties ($r=3-6{\times}10^{-4}{\Omega}.cm$). The optical and electrical properties of the TCO are influenced by the texturing conditions such as not only etchant dilutions but also etching time. We obtained the haze value of 14-16 resulting in increase in light trapping and short-circuit currents also.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.204-205
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• 2011

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 a most widely used thin film deposition process for a-Si:H or ${\mu}c$-Si:H solar cells. For best performance of thin film silicon solar cell, the dopant profiles at p/i and i/n interfaces need to be as sharp as possible. The sharpness of dopant profiles can easily achieved when using multi-chamber PECVD equipment, in which each layer is deposited in separate chamber. However, in a 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 a single-chamber PECVD system in spite of the advantage of lower initial investment cost for the equipment. In order to resolve the cross-contamination problem in single-chamber PECVD systems, flushing method of the chamber with NH3 gas or water vapor after doped layer deposition process has been used. In this study, a new plasma process to solve the cross-contamination problem in a single-chamber PECVD system was suggested. A single-chamber VHF-PECVD system was used for superstrate type p-i-n a-Si:H solar cell manufacturing on Asahi-type U FTO glass. A 80 MHz and 20 watts of pulsed RF power was applied to the parallel plate RF cathode at the frequency of 10 kHz and 80% duty ratio. A mixture gas of Ar, H2 and SiH4 was used for i-layer deposition and the deposition pressure was 0.4 Torr. For p and n layer deposition, B2H6 and PH3 was used as doping gas, respectively. The deposition temperature was $250^{\circ}C$ and the total p-i-n layer thickness was about $3500{\AA}$. In order to remove the deposited B inside of the vacuum chamber during p-layer deposition, a high pulsed RF power of about 80 W was applied right after p-layer deposition without SiH4 gas, which is followed by i-layer and n-layer deposition. Finally, Ag was deposited as top electrode. The best initial solar cell efficiency of 9.5 % for test cell area of 0.2 $cm^2$ could be achieved by applying the in-situ plasma cleaning method. The dependence on RF power and treatment time was investigated along with the SIMS analysis of the p-i interface for boron profiles.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.67-67
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• 2011

Compound semiconductor/CNTs composites have shown considerably improved efficiency improvement in photovoltaic devices, which is often attributed to two different factors. One is the formation of efficient electronic energy cascade structures. The other effect of CNTs on the performance of photovoltaic devices is the decrement of interfacial resistance. The interfacial resistances at n-type/ p-type materials and/or n-type materials/TCO electrode are reduced by an outstanding electrical property of CNTs. In addition to the effects of CNTs, we report the third reason for increment of efficiency in photovoltaic devices by CNT's well-known electrical field enhancement effects. The improved ${\beta}$ values in reverse-FE currents of CIGS electrode with SWNTs layers indicate the enhancement of electrical field in photovoltaic devices, which implies the acceleration of the electron transfer rate in the cell. Due to the formation of an efficient electronic energy cascade structure and the decrease of the interfacial resistance as well as the improvement of the electrical field in the photovoltaic devices, the power conversion efficiency of electrochemically deposited superstrate-type CIGS solar cells was increased 24.3% in the presence of SWNTs and showed 10.40% conversion efficiency.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.665-665
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• 2013

박막형 태양전지에서 광흡수층으로 널리 쓰이는 metal chalcogenide 화합물 중, CuInS2(CIS)은 전기적, 광학적 특성이 우수하여 널리 연구되고 있다. CIS계 태양전지 최근 동시 증발법을 이용하여 20.3%의 고효율을 기록한 바 있으나 기존 진공, 고온 기반 공정 기술은 초기 투자 비용이 높고, 고가의 희귀원소인 In 등의 원료 활용도가 떨어져 원가 절감에 있어 한계가 있다. 이에 따라 제조 비용 절감과 원료 사용 효율을 향상시키기 위해 비진공 방식을 이용한 광흡수 층 증착 공정에 관한 연구가 활발히 진행되고 있다. 본 연구에서는 상온, 상압, 저온에서 합성이 가능한 CIS계 광흡수층을 전자 전달 및 빛 포집에 유리한 ZnO 나노구조와 응용함으로써 superstrate 구조의 박막형 태양전지를 구현하고 그 특성을 평가하였다. CIS 박막 태양전지에서 투명창층으로 쓰이는 ZnO 박막을 수열합성법으로 합성된 ZnO 나노로드 어레이로 대체하여 빛 산란 효과를 줄이고, 전하 수집 및 이동 효과를 극대화하였다. 또한 CIS 광흡수층은amine계 용매와 금속염 및 thiourea를 조합하여 저온에서 코팅 후 건조시켜 박막을 제조하였다. 각 요소 박막들의 물성을SEM, XRD, UV-transmittance 분석을 통해 살펴보았으며, 소면적 태양전지 제작을 통해 박막 구조 대비 30배 이상의 광변환효율(최고효율 3.30%)을 기록하였다.