• Current Photovoltaic Research
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• v.3 no.4
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• pp.107-111
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• 2015

Current characteristic curve of an illuminated solar cell was used to determine its reverse saturation current density ($J_0$), ideality factor (n) and resistances, by using numerical diode simulation. High efficiency amorphous silicon, heterojunction crystalline Si (HIT), plastic and organic-inorganic halide perovskite solar cell shows n=3.27 for a-Si and n=2.14 for improved HIT cell as high and low n respectively, while the perovskite and plastic cells show n=2.56 and 2.57 respectively. The $J_0$ of these cells remain within $7.1{\times}10^{-7}$ and $1.79{\times}10^{-8}A/cm^2$ for poorer HIT and improved perovskite solar cell respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.50-50
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• 2008

ZnO has been extensively studied for optoelectronic applications such as blue and ultraviolet (UV) light emitters and detectors, because it has a wide band gap (3.37 eV) anda large exciton binding energy of ~60 meV over GaN (~26 meV). However, the fabrication of the light emitting devices using ZnO homojunctions is suffered from the lack of reproducibility of the p-type ZnO with high hall concentration and mobility. Thus, the ZnO-based p-n heterojunction light emitting diode (LED) using p-Si and p-GaN would be expected to exhibit stable device performance compared to the homojunction LED. The n-ZnO/p-GaN heterostructure is a good candidate for ZnO-based heterojunction LEDs because of their similar physical properties and the reproducibleavailability of p-type GaN. Especially, the reduced lattice mismatch (~1.8 %) and similar crystal structure result in the advantage of acquiring high performance LED devices with low defect density. However, the electroluminescence (EL) of the device using n-ZnO/p-GaN heterojunctions shows the blue and greenish emissions, which are attributed to the emission from the p-GaN and deep-level defects. In this work, the n-ZnO:Ga/p-GaN:Mg heterojunction light emitting diodes (LEDs) were fabricated at different growth temperatures and carrier concentrations in the n-type region. The effects of the growth temperature and carrier concentration on the electrical and emission properties were investigated. The I-V and the EL results showed that the device performance of the heterostructure LEDs, such as turn-on voltage and true ultraviolet emission, developed through the insertion of a thin intrinsic layer between n-ZnO:Ga and p-GaN:Mg. This observation was attributed to a lowering of the energy barriers for the supply of electrons and holes into intrinsic ZnO, and recombination in the intrinsic ZnO with the absence of deep level emission.

• Korean Journal of Materials Research
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• v.21 no.12
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• pp.666-672
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• 2011

The a-Si:H/c-Si hetero-junction (HJ) solar cells have a variety of advantages in efficiency and fabrication processes. It has already demonstrated about 23% in R&D scale and more than 20% in commercial production. In order to further reduce the fabrication cost of HJ solar cells, fabrication processes should be simplified more than conventional methods which accompany separate processes of front and rear sides of the cells. In this study, we propose a simultaneous deposition of intrinsic thin a-Si:H layers on both sides of a wafer by dual hot wire CVD (HWVCD). In this system, wafers are located between tantalum wires, and a-Si:H layers are simultaneously deposited on both sides of the wafer. By using this scheme, we can reduce the process steps and time and improve the efficiency of HJ solar cells by removing surface contamination of the wafers. We achieved about 16% efficiency in HJ solar cells incorporating intrinsic a-Si:H buffers by dual HWCVD and p/n layers by PECVD.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.6
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• pp.377-385
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• 2018

For the investigation of dopant profiles in implanted $Si_{1-x}Ge_x$, the implanted B and As profiles are measured using SIMS (secondary ion mass spectrometry). The fundamental ion-solid interactions of implantation in $Si_{1-x}Ge_x$ are discussed and explained using SRIM, UT-marlowe, and T-dyn programs. The annealed simulation profiles are also analyzed and compared with experimental data. In comparison with the SIMS data, the boron simulation results show 8% deviations of $R_p$ and 1.8% deviations of ${\Delta}R_p$ owing to relatively small lattice strain and relaxation on the sample surface. In comparison with the SIMS data, the simulation results show 4.7% deviations of $R_p$ and 8.1% deviations of ${\Delta}R_p$ in the arsenic implanted $Si_{0.2}Ge_{0.8}$ layer and 8.5% deviations of $R_p$ and 38% deviations of ${\Delta}R_p$ in the $Si_{0.5}Ge_{0.5}$ layer. An analytical method for obtaining the dopant profile is proposed and also compared with experimental and simulation data herein. For the high-speed CMOSFET (complementary metal oxide semiconductor field effect transistor) and HBT (heterojunction bipolar transistor), the study of dopant profiles in the $Si_{1-x}Ge_x$ layer becomes more important for accurate device scaling and fabrication technologies.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.82.1-82.1
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• 2010

수소화된 비정질 실리콘 박막을 이용한 반도체는 현재 태양전지, 트랜지스터, 매트릭스 배열 및 이미지 센서 등의 분야에서 이용되고 있다. 자세히 이야기 하면, 여러 가지의 광전효과 물질에 대한 특성이 있으며, 가시광선영역에 대하여 > $10^5cm^{-1}$이상의 매우 높은 광흡수계수와 낮은 온도를 갖는 증착공정 등이 있다. 박막의 밴드갭은 약 1.6~1.8eV로서 태양전지의 흡수층과 passivation층으로 적절하다. 여러 가지 종류의 태양전지 중 비정질 실리콘 박막/결정질 실리콘 기판의 구조로 이루어진 이종접합 태양전지는 저온에서 공정이 가능한 대표적인 것으로서 HIT(Heterojunction with Intrinsic Thin layer)구조로 산요사에 의해 제안된 것이다. 이것은 결정질 실리콘 기판과 도핑된 비정질 실리콘 박막사이에 얇은 진성층 비정질실리콘 박막을 삽입함으로서, 캐리어 전송을 좋게하여 실리콘 기판 표면의 passivation효과를 증대시키는 결과를 가지고 온다. 실험실 규모에서는 약 20%이상의 효율을 보이고 있으며, 모듈에서는 19.5%의 높은 효율을 보이고 있어 실리콘 기판을 이용한 고효율 태양전지로서 각광을 받고 있다. 이러한 이종접합 태양전지의 대부분은 단결정 실리콘을 사용하고 있는데, 점차적으로 다결정 실리콘 기판으로 추세가 바뀌고 있어, 여기에 맞는 표면 passivation 공정 및 분석이 필요하다. 본 발표에서는 다결정 실리콘 기판위에 진성층 비정질 실리콘 박막을 유도결합 플라즈마 화학기상 증착법(ICP-CVD)을 이용하여 제조하여 passivation 효과를 분석한다. 일반적으로 ICP는 CCP(coupled charged plasma)에 비해 약 100배 이상 높은 플라즈마 밀도를 가지고 있으며, 이온 충돌같은 표면으로 작용하는 것들이 기존 방식에 비해서 작다라는 장점이 있다. 먼저, 유리기판을 사용하여 ICP-CVD 챔버내에 이송 한 후 플라즈마 파워, 온도 및 가스비(SiH4/H2)에 따른 진성층 비정질 실리콘 박막을 증착 한 후, 밴드갭, 전도도 및 결합구조 등에 대한 결과를 분석한 후, 최적의 값을 가지고 250um의 두께를 갖는 다결정 실리콘을 기판위에 증착을 한다. 두께(1~20nm)에 따라 표면의 passivation이 되는 정도를 QSSPCD(Quasi steady state Photoconductive Decay)법에 의하여 소수캐리어의 이동거리, 재결합율 및 수명 등에 대한 측정 및 분석을 통하여 다결정 실리콘 기판의 passivation effect를 확인한다. 제시된 데이터를 바탕으로 향후 다결정 HIT셀 제조를 통해 태양전지 효율에 대한 특성을 비교하고자 한다.

• Journal of the Korean Solar Energy Society
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• v.38 no.1
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• pp.25-36
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• 2018

The stoichiometric mixture of evaporating materials for the $CaAl_2Se_4$: Co single crystal thin film was prepared from horizontal furnace. Using extrapolation method of X-ray diffraction patterns for the polycrystal $CaAl_2Se_4$, it was found orthorhomic structure whose lattice constant $a_0$, $b_0$ and $c_0$ were 6.4818, $11.1310{\AA}$ and $11.2443{\AA}$, respectively. To obtain the $CaAl_2Se_4$: Co single crystal thin film, $CaAl_2Se_4$: Co mixed crystal was deposited on throughly etched Si (100) by the HWE (Hot Wall Epitaxy) system. The source and substrate temperature were $600^{\circ}C$ and $440^{\circ}C$ respectively. The crystalline structure of $CaAl_2Se_4$: Co single crystal thin film was investigated by the double crystal X-ray diffraction (DCXD). Hall effect on this sample was measured by the method of Van der Pauw and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by impurity scattering in the temperature range 30 K to 100 K and by lattice scattering in the temperature range 100 K to 293 K. The temperature dependence of the energy band gap of the $CaAl_2Se_4$: Co obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=3.8239eV-(4.9823{\times}10^{-3}eV/K)T_2/(T+559K)$. The open-circuit voltage, short current density, fill factor, and conversion efficiency of $p-Si/p-CaAl_2Se_4$: Co heterojunction solar cells under $80mW/cm^2$ illumination were found to be 0.42 V, $25.3mA/cm^2$, 0.75 and 9.96%, respectively.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.682-687
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• 2014

We have performed reverse gate bias stress tests on AlGaN/GaN-on-Si Heterostructure FETs (HFETs). The shift of threshold voltage ($V_{th}$) and the reduction of on-current were observed from the stressed devices. These changes of the device parameters were not permanent. We investigated the temporary behavior of the stressed devices by analyzing the temperature dependence of the instabilities and TCAD simulation. As the baseline temperature of the electrical stress tests increased, the changes of the $V_{th}$ and the on-current were decreased. The on-current reduction was caused by the positive shift of the $V_{th}$ and the increased resistance of the gate-to-source and the gate-to-drain access region. Our experimental results suggest that electron-trapping effect into the shallow traps in devices is the main cause of observed instabilities.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.107-107
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• 2011

오늘 날 transparent conductive oxide는 다양한 분야에서 활용되고 있다. 최근에는 태양전지 분야에서도 많이 활용되고 있으며, 초기에는 transmittance 및 낮은 sheet resistance 특성을 가지는 ITO가 많이 활용되었지만 thin film solar cell와 같이 hydrogenation 공정에 약한 ITO보다는 Al-doped ZnO가 사용되기 시작하면서 많은 연구가 진행되고 있다. 본 연구에서는 thin film solar cell 및 silicon heterojunction solar cell에 적용 가능한 Al-doped ZnO에 관한 연구로써 a-Si:H의 Si-H bonds에 영향을 주지 않는 낮은 영역의 substrate temperature와 power로 Al-doped ZnO를 형성하고 상기 parameter에 따른 Al-doped ZnO의 특성 변화에 대해서 분석하였다. 특히 substrate temperature가 변화할수록 carrier concentration 및 sheet resistance가 많은 변화를 보였으며 이로 인하여 transmittance 특성이 온도에 따라 좋아지다가 너무 높은 온도에서는 오히려 좋지 않게 되었다. 이는 너무 높은 carrier concentration은 free carrier absorption에 의해 transmittance 특성을 오히려 좋지 않게 한다. 우리는 본 연구를 통해 92.677% (450 nm), 90.309% (545 nm), 94.333% (800 nm)의 transmittance를 얻을 수 있었다.

• Macromolecular Research
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• v.14 no.5
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• pp.524-529
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• 2006

New, thermally robust, arylenevinylene conjugated polymers, including poly(9,9-dioctylfluorenyl-2,7-vinylene) [poly(FV)] and poly[2-(3'-dimethyldodecylsilylphenyl)-1,4-phenylenevinylene] [poly(m-SiPhPV)], were synthesized and used for the fabrication of efficient photovoltaic cells. Bulk heterojunction photovoltaic cells fabricated by blending one of the polymers, [poly(FV)], [poly(m-SiPhPV)], and poly(FV-co-m-SiPhPV), with the fullerene derivative [6,6]-phenyl-$C_{61}$-butyric acid methyl ester (PCBM) were found to have a power conversion efficiency of up to 0.038%..

• Current Photovoltaic Research
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• v.7 no.3
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• pp.76-84
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• 2019

Silicon heterojunction solar cells (SHJ) have dominated the photovoltaic market up till now but their conversion performance is practically limited to around 26% compared with the theoretical efficiency limit of 29.4%. A silicon based multi-junction devices are expected to overcome this limitation. In this report, we briefly review the state-of-art characteristic of wide-gap materials which has played a role as top sub-cells in silicon based multi-junction solar cells. In addition, we indicate significantly practical challenges and key issues of these multi-junction combination. Finally, we focus to some characteristics of III-V/c-Si tandem configuration which are reaching highly record performance in multi-junction silicon solar cells.