• Applied Microscopy
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• 제45권3호
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• pp.183-188
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• 2015

Due to the miniaturization of semiconductor devices, their crystal structure on the nanoscale must be analyzed. However, scanning electron microscope-electron backscatter diffraction (EBSD) has a limitation of resolution in nanoscale and high-resolution electron microscopy (HREM) can be used to analyze restrictive local structural information. In this study, three-dimensional (3D) automated crystal orientation and phase mapping using transmission electron microscopy (TEM) (3D TEM-EBSD) was used to identify the crystal structure relationship between an epitaxially grown CdS interfacial layer and a $Cu(In_xGa_{x-1})Se_2$ (CIGS) solar cell layer. The 3D TEM-EBSD technique clearly defined the crystal orientation and phase of the epitaxially grown layers, making it useful for establishing the growth mechanism of functional nano-materials.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.684-685
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• 2013

p-형 반도체인 Cu(In,Ga)$Se_2$ (CIGS) 광 흡수 층은 이보다 에너지 밴드 간격이 큰 n-형 반도체와 이종 접합을 형성한다. 흡수층과 윈도우층 사이의 결정구조 차이와 밴드갭 에너지 차이를 완화시키기 위해 버퍼층이 필요하다. 버퍼층을 형성하는 물질로 화학적 용액 성장법(Chemical Bath deposition)을 사용한 CdS가 많이 적용되어 왔으나 Cd의 유해성 및 습식 공정으로 인한 연속공정에 대한 어려움이 있다. 따라서 버퍼층을 Cd을 포함하지 않는 ZnS, $In_2S_3$, (Zn, Mg)O 등과 같은 물질로 대체하여 원자층 증착법(Atomic Layer Deposition), 펄스레이져증착법(Pulsed Laser Deposition), 스퍼터링(sputtering) 등과 같은 건식으로 성장시키는 연구가 활발히 진행되고 있다. 본 연구에서는 $ZnO_{1-x}S_x$ ($0.2{\leq}x{\leq}0.4$)를 반응성 스퍼터링으로 증착하여 큰 밴드갭 에너지와 높은 광투과율를 갖는 버퍼층을 제작하였다. CIGS 박막의 손상을 줄여주기 위하여 RF 파워는 240, 200, 150, 100 W로 변화시켰다. CIGS 태양전지의 I-V 측정 결과, RF 파워가 150 W일 때 10.7%의 가장 높은 변환 효율을 보였고, 150 W 이상에서는 파워가 증가할 때 단락전류는 감소하였으며 개방전압은 다소 증가하였다. 반면 100 W에서 단락전류는 다소 증가하는 것에 반해 개방 전압이 급격히 낮아졌다. 이것은 파워에 따라 결합되는 산소의 양이 다르기 때문으로 생각된다.

• 한국전기전자재료학회논문지
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• 제33권3호
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• pp.163-168
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• 2020

We studied the change of photovoltaic properties of a flexible CuIn_xGa(_1-x)Se₂ (CIGS) solar cell fabricated on polyimide by mechanical bending with curvature radii of 75 mm (75R) and 20 mm (20R). The flexible CIGS cells were flattened on a PET film, then placed and forced against the surface of a curved block fabricated with pre-designed curvatures. Both up (compressive) and down (tensile) bending were applied to a specimen of CIGS on PET with curvatures of 75R and 20R for 10,000 times and 2,000 times, respectively. From J-V measurements, we found that the conversion efficiency (Eff.) was reduced by 3% and 4% for up-and down-bending, respectively, at curvature 75R; it was greatly reduced by 15% for curvature 20R in the up-bending. However, the open circuit voltage (V_oc) and short-circuit current density (J_sc) seemed to change little, within 3%, for the applied mechanical stresses. The degradation in Eff. resulted from the deterioration of the series (R_s) and shunt (R_sh) resistances of the solar cell.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.257.1-257.1
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• 2015

Cu(In,Ga)Se2 (CIGS) 박막 태양 전지에서 buffer layer는 CIGS 흡수층과 TCO 사이의 밴드갭 차이에 대한 문제점과 lattice mismatch를 해결하기 위해 필수적이다. 흔히 buffer layer 물질로는 CdS가 가장 많이 사용되고 있으나 Cd의 독성에 관한 문제가 야기되고 있다. 따라서 ZnS(O, OH) buffer layer가 친환경 물질로 기존의 CdS 버퍼 층의 대체 물질로 각광 받고 있으며, 단파장 범위에서 높은 투과율로 인해 wide band gap의 Chalcopyrite 태양 전지에 응용되는 buffer layer로 많은 연구가 이루어지고 있다. 또한 buffer layer를 최적화 하여 carrier lifetime과 양자 효율이 증가시킬 수 있는 특성을 가지고 있다. 이 연구에서는 Cu(In,Ga)Se2 (CIGS) 박막에 화학습식공정 (CBD) 방법을 이용하여 최적화된 ZnS(O, OH)의 증착 조건을 찾고, 고품질의 buffer layer를 제조하기 위한 실험에 초점을 맞췄다. 또한, buffer layer의 막질을 개선하고 균일한 막을 제조하기 위해 processing parameters인 시약의 농도, 제조 시간 및 온도 등의 다양한 변화를 통해 실험을 진행하였다. 그 후 최적화된 ZnS(O, OH) buffer layer의 특성 분석을 위해 X-ray diffraction(XRD), photoluminescence (PL), scanning electron microscope (SEM) and GD-OES을 이용하였고, 이를 통해 제조된 CIGS 박막 태양전지는 light induced current-voltage (LIV) and external quantum efficiency (EQE)를 통해 특성 분석을 실시 하였다. 결과적으로, 제조된 ZnS(O, OH) buffer layer의 $ZnSO4{\cdot}7H2O$의 농도는 0.16 M, Thiourea는 0.5 M, NH4OH는 7.5 M, 그리고 반응 온도는 77.5 oC의 조건 하에 CIGS 기판 위에 균일하고 균열이 없는 ZnS(O, OH) 박막을 제조하였으며 이때 제조된 태양전지의 소자 특성은 Voc = 0.478 V, Jsc = 35.79 mA/cm2, FF = 47.77%, ${\eta}=8,18 %$이다.

• 한국재료학회지
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• 제32권11호
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• pp.481-488
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• 2022

The Cu₂ZnSn(S_xSe_1-x)₄ (CZTSSe) absorbers are promising thin film solar cells (TFSCs) materials, to replace existing Cu(In,Ga)Se₂ (CIGS) and CdTe photovoltaic technology. However, the best reported efficiency for a CZTSSe device, of 13.6 %, is still too low for commercial use. Recently, partially replacing the Zn²⁺ element with a Cd²⁺element has attracting attention as one of the promising strategies for improving the photovoltaic characteristics of the CZTSSe TFSCs. Cd²⁺ elements are known to improve the grain size of the CZTSSe absorber thin films and improve optoelectronic properties by suppressing potential defects, causing short-circuit current (J_sc) loss. In this study, the structural, compositional, and morphological characteristics of CZTSSe and CZCTSSe thin films were investigated using X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF), and Field-emission scanning electron microscopy (FE-SEM), respectively. The FE-SEM images revealed that the grain size improved with increasing Cd²⁺ alloying in the CZTSSe thin films. Moreover, there was a slight decrease in small grain distribution as well as voids near the CZTSSe/Mo interface after Cd²⁺ alloying. The solar cells prepared using the most promising CZTSSe absorber thin films with Cd²⁺ alloying (8 min. 30 sec.) exhibited a power conversion efficiency (PCE) of 9.33 %, J_sc of 34.0 mA/cm², and fill factor (FF) of 62.7 %, respectively.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.309.1-309.1
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• 2013

현재까지 CIGS 박막 태양전지는 습식공정인 화학적 용액성장법을 사용하여 형성된 CdS버퍼층을 적용할 경우에 가장 높은 효율을 보이고 있다. 그러나, Cd의 독성 문제와 진공 공정과 호환되지 않는 습식공정 때문에 비독성 건식 공정 버퍼층에 대한 연구가 활발히 진행되고 있다. 습식 공정 CdS 버퍼층을 대체하기 위하여 CdS에 비해 밴드갭이 커서 단파장에서 광 손실이 적은 ZnS 버퍼층을 cracker 황화법을 이용하여 제작하여 CIGS 박막 태양전지에 적용하였다. ZnS 버퍼층을 성장시키기 위해 DC 스퍼터를 사용하여 Zn 박막을 증착한 후, cracker를 사용하여 황화반응을 시켰다. cracker의 cracking zone 온도에 따른 S 반응성을 ZnS 박막의 투과도 변화를 통하여 관찰하였다. 성장된 ZnS 박막은 X-ray diffraction와 Rutherford backscattering spectrometry을 이용하여 박막의 결정성과 조성을 분석하였고, SEM 측정을 통하여 박막의 단면 및 표면 형상을 관찰하였다. 그리고 reflection electron energy loss spectroscopy 분석을 통해 밴드갭을 측정하였다. $700^{\circ}C$의 cracking zone 온도, 3 nm의 Zn 두께, 1 분의 황화공정 조건에서 제작된 ZnS 박막을 CIGS 태양전지의 버퍼층으로 적용한 결과, 반사방지막 없이 12.6%의 변환효율을 얻었다.

• 한국전기전자재료학회논문지
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• 제30권10호
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• pp.625-630
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• 2017

ZnS was chemically deposited as a buffer layer alternative to CdS, for use as a Cd-free buffer layer in $Cu(In_{1-x}Ga_x)Se_2$ (CIGS) solar cells. The deposition of a thin film of ZnS was carried out by chemical bath deposition, following which the structural and optical properties of the ZnS layer were studied. For the experiments, zinc sulfate hepta-hydrate ($ZnSO_4{\cdot}7H_2O$), thiourea ($SC(NH_2)_2$), and ammonia ($NH_4OH$) were used as the reacting agents. The mole concentrations of $ZnSO_4$ and $SC(NH_2)_2$ were fixed at 0.03 M and 0.8 M, respectively, while that of ammonia, which acts as a complexing agent, was varied from 0.3 M to 3.5 M. By varying the mole concentration of ammonia, optimal values for parameters like optical transmission, deposition rate, and surface morphology were determined. For the fixed mole concentrations of $0.03M\;ZnSO_4{\cdot}7H_2O$ and $0.8M\;SC(NH_2)_2$, it was established that 3.0 M of ammonia could provide optimal values of the deposition rate (5.5 nm/min), average optical transmittance (81%), and energy band gap (3.81 eV), rendering the chemically deposited ZnS suitable for use as a Cd-free buffer layer in CIGS solar cells.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.389-389
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• 2012

Molybdenum is one of the most important materials used as a back ohmic contact for $Cu(In,Ga)(Se,S)_2$ (CIGS) solar cells because it has good electrical properties as an inert and mechanically durable substrate during the absorber film growth. Sputter deposition is the common deposition process for Mo thin films. Molybdenum thin films were deposited on soda lime glass (SLG) substrates using direct-current planar magnetron sputtering technique. The outdiffusion of Na from the SLG through the Mo film to the CIGS based solar cell, also plays an important role in enhancing the device electrical properties and its performance. The structure, surface morphology and electrical characteristics of Mo thin films are generally dependent on deposition parameters such as DC power, pressure, distance between target and substrate, and deposition temperature. The aim of the present study is to show the resistivity of Mo layers, their crystallinity and morphologies, which are influenced by the substrate temperature. The thickness of Mo films is measured by Tencor-P1 profiler. The crystal structures are analyzed using X-ray diffraction (XRD: X'Pert MPD PRO / Philips). The resistivity of Mo thin films was measured by Hall effect measurement system (HMS-3000/0.55T). The surface morphology and grain shape of the films were examined by field emission scanning electron microscopy (FESEM: Hitachi S-4300). The chemical composition of the films was obtained by the energy dispersive X-ray spectroscopy (EDX). Finally the optimum substrate temperature as well as deposition conditions for Mo thin films will be developed.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.35.1-35.1
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• 2011

New photovoltaic (PV) materials and manufacturing approaches are needed for meeting the demand for lower-cost solar cells. The prototypal thin-film photovoltaic absorbers (CdTe and $Cu(In,Ga)Se_2$) can achieve solar conversion efficiencies of up to 20% and are now commercially available, but the presence of toxic (Cd,Se) and expensive elemental components (In, Te) is a real issue as the demand for photovoltaics rapidly increases. To overcome these limitations, there has been substantial interest in developing viable alternative materials, such as $Cu_2ZnSnS_4$ (CZTS) is an emerging solar absorber that is structurally similar to CIGS, but contains only earth abundant, non-toxic elements and has a near optimal direct band gap energy of 1.4~1.6 ev and a large absorption coefficient of ${\sim}10^4\;cm^{-1}$. The CZTS absorber layers are grown and investigated by various fabrication methods, such as thermal evaporation, e-beam evaporation with a post sulfurization, sputtering, non-vacuum sol-gel, pulsed laser, spray-pyrolysis method and electrodeposition technique. In the present work, we report an alternative method for large area deposition of CZTS thin films that is potentially high throughput and inexpensive when used to produce monolithically integrated solar panel modules. Specifically, we have developed an aqueous chemical approach based on chemical bath deposition (CBD) with a subsequent sulfurization heat treatment. Samples produced by our method were analyzed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, absorbance and photoluminescence. The results show that this inexpensive and relatively benign process produces thin films of CZTS exhibiting uniform composition, kesterite crystal structure, and good optical properties. A preliminary solar cell device was fabricated to demonstrate rectifying and photovoltaic behavior.

• 한국재료학회지
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• 제24권8호
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• pp.434-442
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• 2014

Serious environmental problems have been caused by the greenhouse effect due to carbon dioxide($CO_2$) or nitrogen oxides($NO_x$) generated by the use of fossil fuels, including oil and liquefied natural gas. Many countries, including our own, the United States, those of the European Union and other developed countries around the world; have shown growing interest in clean energy, and have been concentrating on the development of new energy-saving materials and devices. Typical non-fossil-fuel sources include solar cells, wind power, tidal power, nuclear power, and fuel cells. In particular, organic solar cells(OSCs) have relatively low power-conversion efficiency(PCE) in comparison with inorganic(silicon) based solar cells, compound semiconductor solar cells and the CIGS [$Cu(In_{1-x}Ga_x)Se_2$] thin film solar cells. Recently, organic cell efficiencies greater than 10 % have been obtained by means of the development of new organic semiconducting materials, which feature improvements in crystalline properties, as well as in the quantum-dot nano-structure of the active layers. In this paper, a brief overview of solar cells in general is presented. In particular, the current development status of the next-generation OSCs including their operation principle, device-manufacturing processes, and improvements in the PCE are described.