• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.431-431
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• 2016

Typical Cu(In,Ga)Se2 (CIGS)-based solar cells have a buffer layer between CIGS absorber layer and transparent ZnO front electrode, which plays an important role in improving the cell performance. Among various buffer materials, chemical bath deposition (CBD)-ZnS is being steadily studied to alternative to conventional CdS and the efficiency of CBD-ZnS/CIGS solar cell shows the comparable values with that of CdS/CIGS solar cell. The intriguing thing is that reversible changes occur after exposure to illumination due to the metastable defect states in completed ZnS/CIGS solar cell, which induces an improvement of solar cell performance. Thus, it implies that the understanding of metastable defects in CBD-ZnS/CIGS solar cell is important issue. In this study, we fabricate the ITO/i-ZnO/CBD-ZnS/CIGS/Mo/SLG solar cells by controlling the NH4OH mole concentration (from 2 M to 3.5 M) of CBD-ZnS buffer layer and observe their conversion efficiency with and without light soaking for 1 hr. From the results, NH4OH mole concentration and light exposure can significantly affect the CBD-ZnS/CIGS solar cell performance. In order to investigate that which layer can contain metastable defect states to influence on solar cell performance, impedance spectroscopy and capacitance profiling technique with exposure to illumination have been applied to CBD-ZnS/CIGS solar cell. These techniques give a very useful information on the density of states within the bandgap of CIGS, free carriers density, and light-induced metastable effects. Here, we present the rearranged charge distribution after exposure to illumination and suggest the origin of the metastable defect states in CBD-ZnS/CIGS solar cell.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.106.1-106.1
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• 2011

The Cu(In,Ga)Se2 (CIGS) thin film solar cells have been achieved until almost 20% efficiency by NREL. These solar cells include chemically deposited CdS as buffer layer between CIGS absorber layer and ZnO window layer. Although CIGS solar cells with CdS buffer layer show excellent performance, 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. Among Cd-free candidate materials, the CIGS thin film solar cells with ZnS buffer layer seem to be promising with 17.2%(module by showa shell K.K.), 18.6%(small area by NREL). However, ZnS/CIGS solar cells still show lower performance than CdS/CIGS solar cells. There are several reported reasons to reduce the efficiency of ZnS/CIGS solar cells. Nakada reported ZnS thin film had many defects such as stacking faults, pin-holes, so that crytallinity of ZnS thin film is poor, compared to CdS thin film. Additionally, it was known that the hetero-interface between ZnS and CIGS layer made unfavorable band alignment. The unfavorable band alignment hinders electron transport at the heteo-interface. In this study, we focused on growing defect-free ZnS thin film and for favorable band alignment of ZnS/CIGS, bandgap of ZnS and CIGS, valece band structure of ZnS/CIGS were modified. Finally, we verified the photovoltaic properties of ZnS/CIGS solar cells.

• Current Photovoltaic Research
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• v.8 no.3
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• pp.94-101
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• 2020

This study was trying to focus on achieving high efficiency of multi junction solar cell with thin film silicon solar cells. The proposed thin film Si-Ge/c-Si tandem junction solar cell concept with a combination of low-cost thin-film silicon solar cell technology and high-efficiency c-Si cells in a monolithically stacked configuration. The tandem junction solar cells using amorphous silicon germanium (a-SiGe:H) as an absorption layer of upper sub-cell were simulated through ASA (Advanced Semiconductor Analysis) simulator for acquiring the optimum structure. Graded Ge composition - effect of E_g profiling and inserted buffer layer between absorption layer and doped layer showed the improved current density (J_sc) and conversion efficiency (η). 13.11% conversion efficiency of the tandem junction solar cell was observed, which is a result of showing the possibility of thin film Si-Ge/c-Si tandem junction solar cell.

• Korean Chemical Engineering Research
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• v.55 no.1
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• pp.93-98
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• 2017

This experiment investigated characteristic changes in a $Cu_2ZnSnS_4$(CZTS) solar cell by applying a $Zn(O_x,S_{1-x})$ butter layer with various compositions on the upper side of the absorber layer. Among the four single layers such as $Zn(O_{0.76},S_{0.24})$, $Zn(O_{0.56},S_{0.44})$, $Zn(O_{0.33},S_{0.67})$, and $Zn(O_{0.17},S_{0.83})$, the $Zn(O_{0.76},S_{0.24})$ buffer layer was applied to the device due to its bandgap structure for suppressing electron-hole recombination. In the application of the $Zn(O_{0.76},S_{0.24})$ buffer layer to the device, the buffer layer in the device showed the composition of $Zn(O_{0.7},S_{0.3})$ because S diffused into the buffer layer from the absorber layer. The $Zn(O_{0.7},S_{0.3})$ buffer layer, having a lower energy level ($E_V$) than a CdS buffer layer, improved the $J_{SC}$ and $V_{OC}$ characteristics of the CZTS solar cell because the $Zn(O_{0.7},S_{0.3})$ buffer layer effectively suppressed electron-hole recombination. A substitution of the CdS buffer layer by the $Zn(O_{0.7},S_{0.3})$ buffer layer improved the efficiency of the CZTS solar cell from 2.75% to 4.86%.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.218-218
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• 2011

The CIGS Solar Cells have the highest conversion efficiency in the film-type solar cells. They consist of p-type CuInSe2 film and n-type ZnO film. The CdS films are used as buffer layer in the CIGS solar cells since remarkable difference in the lattice constant and energy band gap of two films. The CdS films are toxic and make harmful circumstances. The CdS films deposition process need wet process. In this works, we design and make the hitter and lamp reflection part in the sputtering system for the ZnS films deposition as buffer layer, not using wet process. Film thickness, SEM, and AFM are measured for the uniformity valuation of the ZnS films. We conclude the optimum deposition temperature for the films uniformity less than 1.6%. The ZnS films deposited by the sputtering system are more dense and uniform than the CdS films deposited by the Chemical Bath Deposition Method(CBD) for the CIGS Solar Cells.

• Current Applied Physics
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• v.18 no.12
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• pp.1592-1599
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• 2018

The present study deals with the effect of dual cathode buffer layer (CBL) on the performance of bilayer of 4,4'-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) and fullerene (C70)-based organic solar cell (OSC) with low donor concentration. OSC devices with CBLs have been fabricated using thermal vapor deposition technique. We report the use of lithium fluoride (LiF) and molybdenum trioxide ($MoO_3$) as CBLs. The insertion of LiF between C70 and aluminium (Al) electrode enhances the power conversion efficiency (PCE) of device from 1.89% to 2.47% but quenching of photogenerated excitons is observed at interface of C70 and LiF layers. Incorporation of $MoO_3$ between LiF and Al electrode further enhances PCE of device to 3.51%. This has also improved the material quality and device properties, by preventing the formation of gap states and diminishing exciton quenching.

• ETRI Journal
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• v.37 no.6
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• pp.1129-1134
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• 2015

In this article, a study of a flower like nanostructured CdS buffer layer for improving the performance of a submicron-thick $CuIn_{1-x}Ga_xSe_2$ (CIGS) solar cell (SC) is presented. Both its synthesis and properties are discussed in detail. The surface reflectance of the device is dramatically decreased. SCs with flower like nanostructured CdS buffer layers enhance short-circuit current density, fill factor, and open-circuit voltage. These enhancements contribute to an increase in power conversion efficiency of about 55% on average compared to SCs that don't have a flower like nanostructured CdS buffer layer, despite them both having the same CIGS light absorbing layer.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.93.2-93.2
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• 2010

Recently, printing and coating technologies application fields have been expanded to the energy field such as solar cell. One of the main reasons, why many researchers have been interested in printing technology as a manufacturing method, is the reduction of manufacturing cost. In this paper, We fabricated CIGS solar cell thin film layer by doctor blade methods using synthesis of CIS precursor nanoparticles ink on molybdenum (Mo) coated soda-lime glass substrate. Synthesis CIS precursor nanoparticles ink fabrication was mixed Cu, In, Se powder and Ethylenediamine, using microwave and centrifuging. Using multi coating process as we could easily fabrication a fine flatness CIS thin-film layer ($0.7{\sim}1.35{\mu}m$), and reduce a manufacture cost and process steps. Also if we use printing and coating method and solution process in each layer of CIGS solar cell (electrode, buffer), it is possible to fabricate all printed thin-film solar cell.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.377-377
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• 2011

Organic solar cells (OSCs) with low cost have been studied to apply on flexible substrate by solution process in low temperature [1]. In previous researches, conventional organic solar cell was composed of metal oxide anode, buffer layer such as PEDOT:PSS, photoactive layer, and metal cathode with low work function. In this structure, indium tin oxide (ITO) and Al was generally used as metal oxide anode and metal cathode, respectively. However, they showed poor reliability, because PEDOT:PSS was sensitive to moisture and air, and the low work function metal cathode was easily oxidized to air, resulting in decreased efficiency in half per day [2]. Inverted organic solar cells (IOSCs) using high work function metal and buffer layer replacing the PEDOT:PSS have focused as a solution in conventional organic solar cell. On the contrary to conventional OSCs, ZnO and TiO2 are required to be used as a buffer layer, since the ITO in IOSC is used as cathode to collect electrons and block holes. The ZnO is expected to be excellent electron transport layer (ETL), because the ZnO has the advantages of high electron mobility, stability in air, easy fabrication at room temperature, and UV absorption. In this study, the IOSCs based on poly [N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) : [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) were fabricated with the ZnO electron-transport layer and MoO3 hole-transport layer. Thickness of the ZnO for electron-transport layer was controlled by rotation speed in spin-coating. The PCDTBT and PC70BM were mixed with a ratio of 1:2 as an active layer. As a result, the highest efficiency of 2.53% was achieved.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.394-396
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• 2012

Chemical bath deposition (CBD) process conditions for depositing CdS buffer layers was studied for high efficiencies of CIGS thin film solar cells. Growth rate of CdS thin films has an effect on surface morphology and quality of thin films. By the change of growth rate, CdS buffer layers showed a large difference in surface morphology and this difference was closely related with the photovoltaic properties of CIGS solar cells.