• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.71.2-71.2
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• 2010

CIS(CuInSe2)계 화합물 태양전지는 높은 광흡수계수와 열적 안정성으로 고효율의 태양전지 제조가 가능하여 화합물 태양전지용 광흡수층으로서 매우 이상적이다. 또한 In 일부를 Ga으로 치환하여 밴드갭을 조절할 수 있는 장점이 있다. 미국 NREL에서는 Co-evaporation 방법을 이용해 20%의 에너지 변환 효율을 달성하였다고 보고된바가 있다. 본 연구에서는 미국의 NREL과 같은 3 stage 방식을 이용하여 광흡수층을 제조하고자 한다. 본 실험에서는 Se 증기압을 각각 $200^{\circ}C$, $230^{\circ}C$, $240^{\circ}C$, $245^{\circ}C$로 달리 하며 실험을 실시하였다. 이때 1st stage의 시간은 15분으로 고정하였으며 기판온도는 약 $250^{\circ}C$로 고정 하였다. 2nd stage는 실시간 온도 감지 장치를 이용하여 Cu와 In+Ga의 조성비가 1:1이 되는 시간을 기준으로 Cu의 조성을 30%더 높게 조절하였으며 기판 온도는 약 $520^{\circ}C$로 고정 후 실험을 실시하였다. 3rd stage의 경우 Cu poor 조성으로 조절하기 위해 모든 조건을 10분으로 고정 후 실험을 실시하였다. 각각의 Se 증기압에 따른 물리적, 전기적 특성을 알아보기 위해 FE-SEM, EDS, XRD 분석을 실시하였다. 본 연구에서 기판은 Na이 첨가되어있는 soda-lime glass를 사용 하였으며 후면 전극으로 약60nm 두께의 Mo를 DC Sputtering 방법을 이용해 증착 하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.152-153
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• 2006

The new approach to buffer layer design for CIGS solar cells that permitted to reduce the buffer absorption losses in the short wavelength range and to overcome the disadvantages inherent to Cd-free CIGS solar cells was proposed. A chemical bath deposition method has been used to produce a high duality buffer layer that comprises thin film of CdS and Zn-based film. The double layer was grown on either ITO or CIGS substrates and its morphological, structural and optical properties were characterized. The Zn-based film was described as the ternary compound $ZnS_x(OH)_y$. The composition of the $ZnS_x(OH)_y$ layer was not uniform throughout its thickness. $ZnS_x(OH)_y$/CdS/substrate region was a highly intermixed region with gradually changing composition. The short wavelength cut-off of double layer was shifted to shorter wavelength (400nm) compared to that (520 nm) for the standard CdS by optimization of the double buffer design. The results show the way to improve the light energy collection efficiency of the nearly cadmium-free CIGS-based solar cells.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.46.2-46.2
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• 2011

CuInSe2 (CIS)계 화합물은 3족 원소(Ga, Al) 또는 6족 원소(S)를 첨가하여 밴드갭 조절이 가능하다는 장점을 가지고 있다. 실제로 동시 증발법으로 Ga을 첨가하여 만든 CuIn0.7Ga0.3Se2(CIGS) 태양전지는 약20%의 높은 효율 보이고 있다. 그러나 최고 효율을 달성한 동시 증발법은 대면적화가 어렵다는 점이 상용화의 걸림돌로 작용하고 있다. 따라서, 그 대안으로 대면적화가 용이한 스퍼터링 및 셀렌화 공정 연구가 진행되고 있다. 그러나 스퍼터링/셀렌화 공정은 Cu-In-Ga 금속 전구체의 셀렌화 시 Ga이 Mo쪽으로 이동하여 CIS/CGS 2개의 상으로 형성된다는 큰 단점을 갖고 있다. 이를 해결하기 위해 셀렌화 후 다시 H2S 기체 분위기에서 열처리하여 표면 밴드갭을 증가시키는 공정이 사용되고 있으나, 이는 열처리 과정이 2번 필요하다는 단점을 갖고 있다. 이러한 단점을 해결하고자 본 연구에서는 금속 전구체의 구조, 셀렌화 공정 조건 및 전구체 내의 상(phase) 조절을 통해 셀렌화 시 Ga segregation을 억제하고자 하였다. 특히 전구체의 상 조절을 통해서 Ga의 이동을 크게 완화시킬 수 있음을 확인하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.2
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• pp.102-107
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• 2003

This study puts focus on the optimization of growth temperature of CIGS absorber layer which affects severely the performance of solar cells. The CIGS absorber layers were prepared by three-stage co-evaporation of metal elements in the order of In-Ga-Se. The effect of the growth temperature of 1st stage was found not to be so important, and 350$^{\circ}C$ to be the lowest optimum temperature. In the case of growth temperature at 2nd/3rd stage, the optimum temperature was revealed to be 550$^{\circ}C$. The XRD results of CIGS films showed a strong (112) preferred orientation and the Raman spectra of CIGS films showed only the Al mode peak at 173cm$\^$-1/. Scanning electron microscopy results revealed very small grains at 2nd/3rd stage growth temperature of 480$^{\circ}C$. At higher temperatures, the grain size increased together with a reduction in the number of the voids. The optimization of experimental parameters above mentioned, through the repeated fabrication and characterization of unit layers and devices, led to the highest conversion efficiency of 15.4% from CIGS-based thin film solar cell with a structure of Al/ZnO/CdS/CIGS/Mo/glass.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.295-295
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• 2010

Nanoparticles of the compound semiconductor, Cu(In, Ga)Se2 (CIGS), were synthesized in solution under ambient pressure below $100^{\circ}C$ and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), optical absorption spectroscopy and energy-dispersive X-ray (EDX) analyses. These materials have chalcopyrite crystal structures and the particle sizes less than 100 nm. Synthetic conditions were studied for the crystallized CIGS nanoparticles formation to prevent from side products of Cu2Se, Cu2-xSe, and CuSe etc. The single phase CIGS nanoparticles were applied to coating of thin films photovoltaic cells. The electro deposition of CIGS thin films is also a good non-vacuum technology and under investigation. In aqueous solutions, the different chemical compositions of CIGS thin films were obtained, depending on pH, concentration of starting materials and deposition potentials. The surface morphology of the prepared CIGS thin films depends on the complexing ligands to the solutions during the electrochemical deposition.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.98.2-98.2
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• 2012

Thin film solar cells are growing up in the market due to their high efficiency and low cost. Especially CdTe and $CuInGaSe_2$ based solar cells are leading the other cells, but due to the limited percentage of the elements present in our earth's crust like Tellurium, Indium and Gallium, the price of the solar cells will increase rapidly. Copper Zinc Tin Sulfide (CZTS) and Copper Zinc Tin Selenide (CZTSe) semiconductor (having a kesterite crystal structure) are getting attention for its solar cell application as the absorber layer. CZTS and CZTSe have almost the same crystal structure with more environmentally friendly elements. Various authors have reported growth and characterization of CZTSe films and solar cells with efficiencies about 3.2% to 8.9%. In this study, a novel method to prepare CZTSe has been proposed based on selenization of stacked Copper Selenide ($Cu_2Se$), Tin Selenide ($SnSe_2$) and Zinc Selenide (Zinc Selenide) in six possible stacking combinations. Depositions were carried out through RF magnetron sputtering. Selenization of all the samples was performed in Close Space Sublimation (CSS) in vacuum at different temperatures for three minutes. Characterization of each sample has been performed in Field Emission SEM, XRD, Raman spectroscopy, EDS and Auger. In this study, the properties and results of $Cu_2ZnSnSe_4$ thin films grown by selenization will be presented.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.63-66
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• 2002

Bi-layer Mo films were deposited on sodalime glass substrates using DC magnetron sputtering. As the gas pressure and power density, the resistivity varied from $1.5{\times}10^{-5}$ to $4.97{\times}10^{-4}{\Omega}{\cdot}cm$. Furthermore, stress direction yielded compressive-to-tensile transition stress curves. The microstructure of the compressive stress films which had poor adhesion consists of tightly packed columns, but of the tensile-stressed films had less dense structure. Under all gas pressure conditions, Mo films exhibited distinctly increasing optical reflection with decreasing gas pressure. The expansion of (110) peak width with the gas pressure meant the worse crystalline growth. Also, The highest efficiency was 15.2% on 0.2 $cm^2$. The fill factor, open circuit voltage and short circuit current were 63 %, 570 m V and 42.6 $mA/cm^2$ respectively.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.138-138
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• 2009

Recently, thin-film solar cells of Cu(In,Ga)$Se_2$(CIGS) have reached a high level of performance, which has resulted in a 19.9%-efficient device. These conventional devices were typically fabricated using chemical bath deposited CdS buffer layer between the CIGS absorber layer and ZnO window layer. However, the short wavelength response of CIGS solar cell is limited by narrow CdS band gap of about 2.42 eV. Taking into consideration the environmental aspect, the toxic Cd element should be replaced by a different material. It is why during last decades many efforts have been provided to achieve high efficiency Cd-free CIGS solar cells. In order to alternate CdS buffer layer, ZnS buffer layer is grown by using chemical bath deposition(CBD) technique. The thickness and chemical composition of ZnS buffer layer can be conveniently by varying the CBD processing parameters. The processing parameters were optimized to match band gap of ZnS films to the solar spectrum and exclude the creation of morphology defects. Optimized ZnS buffer layer showed higher optical transmittance than conventional thick-CdS buffer layer at the short wavelength below ~520 nm. Then, chemically deposited ZnS buffer layer was applied to CIGS solar cell as a alternative for the standard CdS/CIGS device configuration. This CIGS solar cells were characterized by current-voltage and quantum efficiency measurement.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.464.1-464.1
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• 2014

Among numerous material candidates, Cu(InxGa1-x)(SySe2-y) (CIGS) thin films have emerged as promising material candidates for thin film solar cell applications due to the high energy conversion efficiency and relatively low fabrication cost. The CIGS thin film solar cells consist of several materials, including Mo back contacts, ZnO-based window layers, and CdS buffer layers. All these materials have different crystal structures and contain quite distinct chemical elements, and hence the device characterization requires careful analyses. Most of all, identification of the major trap states resulting in the carrier recombination processes is a key step toward realization of high efficiency CIGS solar cells. We have carried out electrical investigations of CIGS thin film solar cells to specify the major trap states and their roles in photovoltaic performance. In particular, we have used the temperature-dependent transport characterizations and admittance spectroscopy. In this presentation, we will introduce some exemplary studies of DC and AC electrical characteristics of the CIGS solar cells.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.2
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• pp.125-129
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• 2005

Two kinds of physical treatments were examined for the analysis both of intrinsic surface and interior nature of CuInS $e_2$[CIS] and CuGaS $e_2$[CGS] films grown in separated systems. For the first method, a selenium protection layer which was immediately deposited after the growth of the CIS was investigated. The Se cap layer protects CISe surface from oxidation and contamination during the transport under ambient atmosphere. The Se cap was removed by thermal annealing at temperature above 15$0^{\circ}C$. After the decapping treatment at 2$25^{\circ}C$ for 60 min, ultraviolet photoemission and inverse photoemission measurements of the CIS film showed that its valence band maximum(VBM) and conduction band minimum (CBM) are located at 0.58 eV below and 0.52 eV above the Fermi level $E_{F}$, respectively. For the second treatment, an Ar ion beam etching was exploited. The etching with ion kinetic energy $E_{k}$ above 500 eV resulted in broadening of photoemission spectra of core signals and occasional development of metallic feature around $E_{F}$. These degradations were successfully suppressed by decreasing $E_{k}$ below 400 eV. CGS films etched with the beam of $E_{k}$ = 400 eV showed a band gap of 1.7 eV where $E_{F}$ was almost centered.st centered.