• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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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.

• Journal of Sensor Science and Technology
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• v.13 no.2
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• pp.157-167
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• 2004

A stoichiometric mixture of evaporating materials for $CuAlSe_{2}$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $CuAlSe_{2}$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were $680^{\circ}C$ and $410^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $CuAlSe_{2}$ single crystal thin films measured with Hall effect by van der Pauw method are $9.24{\times}10^{16}cm^{-3}$ and $295cm^{2}/V{\codt}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuAlSe_{2}$ obtained from the absorption spectra was well described by the Varshni's relation, $E_{g}(T)$ = 2.8382 eV - ($8.68{\circ}10^{-4}$ eV/K)$T^{2}$/(T + 155 K). The crystal field and the spin-orbit splitting energies for the valence band of the $CuAlSe_{2}$ have been estimated to be 0.2026 eV and 0.2165 eV at 10 K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}so$ definitely exists in the ${\Gamma}_{5}$ states of the valence band of the $CuAlSe_{2}$. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1-}$, $B_{1-}$, and $C_{1-}$ exciton peaks for n = 1.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.163-163
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• 2011

셀레늄(Selenium: Se) cracker cell을 이용하여 셀렌화한 $CuInSe_2$ (CIS)박막에 대해 연구한 결과를 발표하고자 한다. 화석연료의 과도한 사용으로 지구온난화라는 환경문제가 대두되면서 영구적이고 무상의 태양에너지 이용에 대한 필요성이 점차 높아지고 있다. 빛에너지를 전기에너지로 변화시키기 위한 태양전지는 재료에 따라 다양하게 개발되고 있으며 그 중 가장 주목을 받고 있는 것 중의 하나가 $CuInSe_2$을 광흡수층으로 하는 CIS 박막 태양전지이다. CIS 박막은 태양전지의 광흡수층으로 사용되는데 직접천이형 밴드구조를 가지고 있고, 약 $10^5$ $cm^{-1}$의 높은 광흡수계수를 가지고 있어 태양전지 광흡수층으로 적합한 물질로 각광받고 있다. CIS는 에너지 밴드갭이 ~1 eV로 실리콘과 유사한 밴드갭을 가지고 있으나 이는 Ga, Al을 In 대신 치환함으로 조절할 할 수 있다. 무엇보다도 sodalime 유리와 같은 저가의 기판위에 스퍼터와 같은 장치로 대면적 CIS 박막태양전지를 만들 수 있다는 것이 산업적인 면에서 장점으로 알려져 있다. 본 연구에서는 sodalime 유리기판 위에 스퍼터 방법으로 CIS 박막을 증착하고 Se cracker cell로 셀렌화하여 CIS 박막을 제조하는 것을 조사연구 하였다. 스퍼터를 이용하여 유리기판위에 Mo (Molybdenum)을 증착하고 그 위에 Cu-In-Se박막을 증착하였다. Cu-In-Se/Mo/유리기판 시료는 동일 챔버에서 Se cracker cell을 이용하여 셀렌화 처리 하였다. 물성비교를 위하여 Knudson-cell을 이용한 셀렌화도 시행하였다. Se cracker cell은 고체 Se를 가열하는 부분(R-zone)과 Se flux를 cracking 하는 부분(C-zone)으로 나누어져 있으며 C-zone은 700$^{\circ}C$로 고정하였다. 셀렌화 기판 온도는 425$^{\circ}C$로 고정하였고 Se cracker 온도는 330~375$^{\circ}C$까지 변화시켜 가며 CIS 박막을 제조하였다. 제조된 CIS 박막의 물성 조사는 사진, 현미경, SEM, EDX, XRD, Hall effects를 이용하였다. Se cracker cell로 셀렌화한 CIS 박막은 island 구조를 하고 있음을 알 수 있었다. CIS 박막의 island의 크기와 모양은 셀렌화시 R-zone 온도(Cu-In-Se 박막에 조사되는 셀레늄의 량)에 큰 영향을 받았다. 셀렌화시 셀레늄량이 적을 때는 island가 커지며 불균일해지고 셀레늄량이 많을 때 island가 작고 균일해지는 경향을 SEM을 통해 관찰할 수 있었다. X-ray 회절을 통해 셀레늄량이 적을 경우 CIS 결정이외의 결정이 박막내에 형성됨을 알 수 있었다. 학술회의에서 Se cracker cell을 이용한 셀렌화에 관한 보다 깊은 연구결과를 발표하고자 한다.

• Ceramist
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• v.22 no.2
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• pp.146-169
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• 2019

To overcome the theoretical efficiency of single-junction solar cells (> 30 %), tandem solar cells (or multi-junction solar cells) is considered as a strong nominee because of their excellent light utilization. Organic-inorganic halide perovskite has been regarded as a promising candidate material for next-generation tandem solar cell due to not only their excellent optoelectronic properties but also their bandgap-tune-ability and low-temperature process-possibility. As a result, they have been adopted either as a wide-bandgap top cell combined with narrow-bandgap silicon or CuIn_xGa_(1-x)Se₂ bottom cells or for all-perovskite tandem solar cells using narrow- and wide-bandgap perovskites. To successfully transition perovskite materials from for single junction to tandem, substantial efforts need to focus on fabricating the high quality wide- and narrow-bandgap perovskite materials and semi-transparent electrode/recombination layer. In this paper, we present an overview of the current research and our outlook regarding perovskite-based tandem solar technology. Several key challenges discussed are: 1) a wide-bandgap perovskite for top-cell in multi-junction tandem solar cells; 2) a narrow-bandgap perovskite for bottom-cell in all-perovskite tandem solar cells, and 3) suitable semi-transparent conducting layer for efficient electrode or recombination layer in tandem solar cells.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.85.1-85.1
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• 2010

$Cu(In,Ga)Se_2$ (CIGS) thin film solar cell is currently 19.5% higher efficiency and developing a large area technology. The structure of CIGS solar cell that make five unit layers as back contact, light absorption, buffer, front transparent conducting electrode and antireflection to make them sequentially forming. Materials and various compositions of thin film unit which also manufacture a variety method used by the physical and chemical method for CIGS solar cell. The construction and performance test of evaporator for CIGS thin film solar cell has been done. The vapor pressures were changed by using vapor flux meter. The vapor pressure were copper (Cu) $2.1{\times}10^{-7}{\sim}3.0{\times}10^{-7}$ Torr, indium (In) $8.0{\times}10^{-7}{\sim}9.0{\times}10^{-7}$ Torr, gallium (Ga) $1.4{\times}10^{-7}{\sim}2.8{\times}10^{-7}$ Torr, and selenium (Se) $2.1{\times}10^{-6}{\sim}3.2{\times}10^{-6}$ Torr, respectively. The characteristics of the CIGS thin film was investigated by using X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and photoluminescence (PL) spectroscopy using a He-Ne laser. In PL spectrum, temperature dependencies of PL spectra were measured at 1137 nm wavelength.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.675-675
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• 2013

CIGS thin films have received a great attention as a promising material for solar cells due to their high absorption coefficient, appropriate bandgap, long-term stability, and low cost production. CIGS thin films have been deposited by various methods such as co-evaporation, sputtering, spray pyrolysis and electro-deposition. In this study, Cu(In,Ga)Se2(CIGS) thin films were prepared using a single quaternary target by rf magnetron sputtering. The effect of sulfurization on the structural, compositional and electrical properties of the films was examined in order to develop the deposition process. An optimal sulfurization process will be selected for the preparation of CIGS thin films with good structural, optical and electrical properties by applying various sulfurization processes. In addition, the electrical properties of CIGS thin films were investigated by post-deposition annealing process. The carrier concentration of CIG(SSe) thin films after sulfurization was increased from $10^{14}cm^{-3}$ to $10^{16}cm^{-3}$ and the resistivity was increased from 10 ${\Omega}cm$ to $10^3$ ${\Omega}cm$. It is confirmed that CIG(SSe) thin films prepared at optimal deposition condition have similar atomic ratio to the target value after sulfurization.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.3
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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.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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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.

• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1473-1476
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• 2013

Solution-based deposition of $CuIn_xGa_{1-x}Se_2$ (CIGSe) thin films is well known non-vacuum process for the fabrication of CIGSe solar cells. However, due to the usage of organic chemicals in the preparation of CIG precursor solutions, the crystallization of the polycrystalline CIGSe and the performance of CIGSe thin film solar cells were significantly affected by the carbon residues from the organic chemicals. In this work, we have tried to eliminate the carbon residues in the CIG precursor thin films efficiently by using soft-annealing process. By adjusting soft-annealing temperature, it is possible to control the amount of carbon residues in CIG precursor thin films. The reduction of the carbon residues in CIG precursors by high temperature soft-annealing improves the grain size and morphology of polycrystalline CIGSe thin films, which are also closely related with the electrical properties of CIGSe thin film solar cells.