• Current Photovoltaic Research
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• v.3 no.1
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• pp.16-20
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• 2015

Ag addition in chalcopyrite materials is known to lead beneficial changes in aspects of structural and electronic properties. In this work, the effects of Ag alloying of $Cu(In,Ga)Se_2$-based solar cells has been investigated. Wide bandgap $(Ag,Cu)(In_{1-x},Ga_x)Se_2$ (x = 0.75~0.8) films have been deposited using a three-stage co-evaporation with various Ag/(Ag+Cu) ratios. With Ag alloying the $(Ag,Cu)(In_{1-x},Ga_x)Se_2$ (x~0.8) films were found to have greater grainsize and film thickness. Device were also fabricated with the $(Ag,Cu)(In_{1-x},Ga_x)Se_2$ (x~0.8) films and their J-V and quantum efficiency measurements were carried out. The highest-efficiency $(Ag,Cu)(In_{1-x},Ga_x)Se_2$ solar cell with Eg > 1.5 eV had an efficiency of 12.2% with device parameters $V_{OC}=0.810V$, $J_{SC}=21.7mA/cm^2$, and FF = 69.0%.

• Korean Journal of Materials Research
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• v.22 no.5
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• pp.259-273
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• 2012

Chalcogenide-based semiconductors, such as $CuInSe_2$, $CuGaSe_2$, Cu(In,Ga)$Se_2$ (CIGS), and CdTe have attracted considerable interest as efficient materials in thin film solar cells (TFSCs). Currently, CIGS and CdTe TFSCs have demonstrated the highest power conversion efficiency (PCE) of over 11% in module production. However, commercialized CIGS and CdTe TFSCs have some limitations due to the scarcity of In, Ga, and Te and the environmental issues associated with Cd and Se. Recently, kesterite CZTS, which is one of the In- and Ga- free absorber materials, has been attracted considerable attention as a new candidate for use as an absorber material in thin film solar cells. The CZTS-based absorber material has outstanding characteristics such as band gap energy of 1.0 eV to 1.5 eV, high absorption coefficient on the order of $10^4cm^{-1}$, and high theoretical conversion efficiency of 32.2% in thin film solar cells. Despite these promising characteristics, research into CZTS-based thin film solar cells is still incomprehensive and related reports are quite few compared to those for CIGS thin film solar cells, which show high efficiency of over 20%. The recent development of kesterite-based CZTS thin film solar cells is summarized in this work. The new challenges for enhanced performance in CZTS thin films are examined and prospective issues are addressed as well.

• Journal of the Korean Vacuum Society
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• v.22 no.1
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• pp.1-6
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• 2013

In this paper, to develop linear source for evaporating $600{\times}1,200mm$ size of large area CIGS absorber layer, we simulated linear thermal source and obtained ${\pm}5%$ thickness uniformity with various nozzle sizes and regular nozzle distance. Flux density was confirmed linear source length. Using this linear source, we tested thickness uniformity of Copper, Indium single layer which was obtained Cu ${\pm}5%$ and In ${\pm}5%$ thickness uniformity. And then CIGS absorber layers were evaporated with In-line single-stage co-evaporation. Large area CIGS absorber layers were confirmed composition uniformity of $$Cu{\leq_-}5%$$, $$In{\leq_-}7%$$, $$Ga{\leq_-}4%$$, $$Se{\leq_-}3%$$ with 600 mm width by XRF. Uniform shape of CIGS absorber layers was confirmed by SEM. XRD showed peaks which indicate chalcopyrite structure of CIGS absorber layers. Thus, developed linear source is suitable for evaporating CIGS absorber layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.158-158
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• 2011

$Cu(In_xGa_{1-x})Se_2$ (CIGS) thin film solar cell is one of the most promising solar cells in photovoltaic devices. CIGS has a direct band gap which varied from 1.0 to 1.26 eV, depending on the Ga to In ratio. Also, CIGS has been studying for an absorber in thin film solar cells due to their highest absorption coefficient which is $1{\times}10^5cm^{-1}$ and good stability for deposition process at high temperature of $450{\sim}590^{\circ}C$. Currently, the highest efficiency of CIGS thin film solar cell is approximately 20.3%, which is closely approaching to the efficiency of poly-silicon solar cell. The deposition technique is one of the most important points in preparing CIGS thin film solar cells. Among the various deposition techniques, the sputtering is known to be very effective and feasible process for mass production. In this study, CIGS thin films have been prepared by rf magnetron sputtering method using a single target. The optical and structural properties of CIGS films are generally dependent on deposition parameters. Therefore, we will explore the influence of deposition power on the properties of CIGS films and the films will be deposited by rf magnetron sputtering using CIGS single target on Mo coated soda lime glass at $500^{\circ}C$. The thickness of CIGS films will be measured by Tencor-P1 profiler. The optical properties will be measured by UV-visible spectroscopy. The crystal structure will be analyzed using X-ray diffraction (XRD). Finally the optimal deposition conditions for CIGS thin films will be developed.

• Current Photovoltaic Research
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• v.2 no.3
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• pp.88-94
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• 2014

The structural, optical and electrical properties of sputter-deposited CIGS films were directly influenced by the sputtering process parameters such as substrate temperature, working pressure, RF power and distance between target and substrate. CIGS thin films deposited by using a quaternary target revealed to be Se deficient due to Se low vapor pressure. This Se deficiency affected the overall stoichiometry of the films, causing the films to be Cu-rich. Current tends to pass through the Cu-Se channels which act as the shunting path increasing the film conductivity. The crystal structure of CIGS thin films depends on the substrate orientation due to the influence of surface morphology, grain size and stress of Mo substrate. The excess of Cu was removed from the CIGS films by KCN treatment, achieving a suitable Cu concentration (referred as Cu-poor) for the fabrication of solar cell. Due to high Cu concentrations on the CIGS film surface induced by Cu-Se phases after CIGS film deposition, KCN treatment proved to be necessary for the fabrication of high efficiency solar cells. Also during KCN treatment, dislocation density and lattice parameter decreased as excess Cu was removed, resulting in increase of bandgap and the decrease of conductivity of CIGS films. It was revealed that Cu-Se secondary phase could be removed by KCN wet etching of CIGS films, allowing the fabrication of high efficiency absorber layer.

• Korean Journal of Materials Research
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• v.25 no.4
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• pp.196-201
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• 2015

This paper presents the impact of partial shading on $CuIn_xGa_{(1-x)}Se_2(CIGS)$ photovoltaic(PV) modules with bypass diodes. When the CIGS PV modules were partially shaded, the modules were under conditions of partial reverse bias. We investigated the characterization of the bypass diode and solar cell properties of the CIGS PV modules when these was partially shaded, comparing the results with those for a crystalline silicon module. In crystalline silicon modules, the bypass diode was operated at a partial shade modules of 1.67 % shading. This protected the crystalline silicon module from hot spot damage. In CIGS thin film modules, on the other hand, the bypass diode was not operated before 20 % shading. This caused damage because of hotspots, which occurred as wormlike defects in the CIGS thin film module. Moreover, the bypass diode adapted to the CIGS thin film module was operated fully at 60% shading, while the CIGS thin film module was not operated under these conditions. It is known that the bypass diode adapted to the CIGS thin film module operated more slowly than that of the crystalline silicon module; this bypass diode also failed to protect the module from damage. This was because of the reverse saturation current of the CIGS thin film, $1.99{\times}10^{-5}A/cm^2$, which was higher than that of crystalline silicon, $8.11{\times}10^{-7}A/cm^2$.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.160-160
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• 2013

본 실험에서는 CIGS 흡수층을 스퍼터링 방식과 급속열처리 장비를 이용한 2-step 방식을 이용하여 형성시켰다. 전구체는 DC 스퍼터링 방법으로 $Cu_{0.75}Ga_{0.25}/In$의 다층 전구체를 구성 후, 독성이 없는 셀레늄 팰릿을 graphite 상자에 넣어 급속열처리 장비로 온도를 $475{\sim}680^{\circ}C$로 온도를 조절하면서 셀렌화 하였다. 이렇게 구성된 CIGS 흡수층의 특성을 scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray differection (XRD)를 통해서 측정을 하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.7
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• pp.503-509
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• 2013

In this study, $Cu(In_{1-x},Ga_x)Se_2$ (CIGS) thin films were prepared on the Mo coated soda-lime glass by the DC magnetron sputtering and a subsequent selenization process. For the selenization process, selenization rapid thermal process(RTP) with cracker cell, which was helpful to smaller an atomic of Se, was adopted. To make CIGS layer, they were then annealed with the cracked Se. Based on this selenization method, we made several CIGS thin film and investigated the effects of In deposition time, and selenization time. Through x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM), it is found that the Mo/In/CuGa structure and the high sputtering power shows the dominant chalcopyrite structure and have a uniform distribution of the grain size. The CIGS films with the In deposition time of 5 min has the best structure due to the smooth surface. And CIGS films with the selenization time of 50 min show good crystalline growth without any voids.

• 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.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.45-46
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• 2015

Se 원소가 포함된 $CuIn_xGa_{1-x}Se_2$(CIGS) 단일 스퍼터링 타겟을 이용하여 후처리 공정없이 단일 스퍼터링 공정만으로 CIGS 흡수층 박막을 증착하여 소자 특성을 확인하였다. 단일 CIGS 흡수층 공정이 적용된 CIGS 박막태양전지 소자(유리기판/Mo/단일 CIGS 흡수층 박막/CdS/i-ZnO/Al-doped ZnO/Ni-Al grid)에서 10.0%의 태양광 변환 효을을 달성하였으며, 이는 기존의 복잡한 공정구조를 해결하여 대면적 양산화 CIGS 제조 공정에도 적용할 수 있음을 확인하였다.