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신동협(Shin, Dong-Hyeop),윤재호(Yun, Jae-Ho),Larina, Liudmila,안병태(Ahn, Byung-Tae) 한국신재생에너지학회 2009 한국신재생에너지학회 학술대회논문집 Vol.2009 No.06
Recently, thin-film solar cells of Cu(In,Ga)Se₂(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.
Shin, Young Min,Lee, Chang Soo,Shin, Dong Hyeop,Ko, Young Min,Al-Ammar, Essam A.,Kwon, Hyuck Sang,Ahn, Byung Tae The Electrochemical Society 2013 ECS journal of solid state science and technology Vol.2 No.6
<P>Cu(In,Ga)Se<SUB>2</SUB> (CIGS) solar cells fabricated on soda-lime glass (SLG) exhibited high efficiency due to the supply of Na from the SLG substrate. As a simple doping method, Na can be supplied into CIGS films using a Na compound deposited on Mo electrodes. In this study, the authors compared the properties of CIGS thin films grown on a NaF layer deposited on Mo-coated Na-free glass with those of CIGS films on Mo-coated SLG by a standard through high-resolution transmission electron microscopy and low-temperature photoluminescence analyzes. After NaF deposition on the Mo film, an amorphous interlayer was detected at the CIGS/MoSe<SUB>2</SUB> interface, and the MoSe<SUB>2</SUB> layer that formed on the Mo surface was thin. The photoluminescence study showed that NaF doping did not effectively prevent the formation of deep donors in the CIGS film, whereas Na supplied by SLG effectively prevents their formation. We concluded that the poor performance of CIGS solar cells incorporating a NaF precursor is due to the amorphous layer at the CIGS/Mo interface and different luminescence characteristic with standard CIGS films, resulting in a low minority carrier collection.</P>
Shin, Young Min,Shin, Dong Hyeop,Kim, Ji Hye,Ahn, Byung Tae Elsevier 2011 Current Applied Physics Vol.11 No.1
<P><B>Abstract</B></P><P>Na doping in CIGS film is one of the most crucial factors that affects the performance of CIGS solar cells. However, the role of Na doping is not yet well understood. In this study, in order to find an effective Na doping method, Na was doped into CIGS film using Na<SUB>2</SUB>S precursor at three different points in the three-stage co-evaporation and its effect on CIGS film was investigated. The microstructures, Na doping profiles and bonding states were examined using scanning electron microscope, x-ray diffraction, secondary ion mass spectroscopy and x-ray photoelectron spectroscopy. It was found that the external sodium doping with Na<SUB>2</SUB>S changed the microstructure and the Na doping profile. The performance of a CIGS solar cell with the external Na doping on Mo/Corning glass was worse than that of a conventional CIGS solar cell fabrication. The best performance achieved by means of Na external doping was 14.2% efficiency, which was achieved when Na was doped by depositing a Na<SUB>2</SUB>S precursor layer on a Mo metal layer.</P>
Mo 기판위의 NaF 중간층을 이용한 Cu(In,Ga)Se<sub>2</sub> 광흡수층의 Na 도핑특성에 관한 연구
박태정,신동협,안병태,윤재호,Park, Tae-Jung,Shin, Dong-Hyeop,Ahn, Byung-Tae,Yun, Jae-Ho 한국재료학회 2009 한국재료학회지 Vol.19 No.8
In high-efficiency Cu(In,Ga)$Se_2$ solar cells, Na is doped into a Cu(In,Ga)$Se_2$ light-absorbing layer from sodalime-glass substrate through Mo back-contact layer, resulting in an increase of device performance. However, this supply of sodium is limited when the process temperature is too low or when a substrate does not supply Na. This limitation can be overcome by supplying Na through external doping. For Na doping, an NaF interlayer was deposited on Mo/glass substrate. A Cu(In,Ga)$Se_2$ absorber layer was deposited on the NaF interlayer by a three-stage co-evaporation process As the thickness of NaF interlayer increased, smaller grain sizes were obtained. The resistivity of the NaF-doped CIGS film was of the order of $10^3{\Omega}{\cdot}cm$ indicating that doping was not very effective. However, highest conversion efficiency of 14.2% was obtained when the NaF thickness was 25 nm, suggesting that Na doping using an NaF interlayer is one of the possible methods for external doping.
Park, Do Hyung,Cho, Yang Hwi,Shin, Dong Hyeop,Ahn, Byung Tae Korea Photovoltaic Society 2013 Current Photovoltaic Research Vol.1 No.2
ZnO film has been used for CIGS solar cells as a buffer layer as itself or by doping Mg and Sn; ZnO film also has been used as a transparent conducting layer by doping Al or B for solar cells. Since ZnO itself is a host material for many applications it is necessary to understand the electrical and optical properties of ZnO film itself with various preparation conditions. We prepared ZnO films by converting ZnS precursor into ZnO film by thermal annealing. ZnO film was formed at low temperature as low as $500^{\circ}C$ by annealing a ZnS precursor layer in air. In the air annealing, the electrical resistivity decreased monotonically with increasing annealing temperature; the intensity of the green photoluminescence at 505 nm increased up to $750^{\circ}C$ annealing. The electrical resistivity further decreased and the intensity of green emission also increased in reducing atmospheres. The results suggest that deep-level defects originated by oxygen vacancy enhanced green emission, which reduce light transmittance and enhance the recombination of electrons in conduction band and holes in valence. More oxidizing environment is necessary to obtain defect-free ZnO film for higher transparency.
Do Hyung Park,Yang Hwi Cho,Dong Hyeop Shin,Byung Tae Ahn 한국태양광발전학회 2013 Current Photovoltaic Research Vol.1 No.2
ZnO film has been used for CIGS solar cells as a buffer layer as itself or by doping Mg and Sn; ZnO film also has been used as a transparent conducting layer by doping Al or B for solar cells. Since ZnO itself is a host material for many applications it is necessary to understand the electrical and optical properties of ZnO film itself with various preparation conditions. We prepared ZnO films by converting ZnS precursor into ZnO film by thermal annealing. ZnO film was formed at low temperature as low as 500°C by annealing a ZnS precursor layer in air. In the air annealing, the electrical resistivity decreased monotonically with increasing annealing temperature; the intensity of the green photoluminescence at 505 nm increased up to 750°C annealing. The electrical resistivity further decreased and the intensity of green emission also increased in reducing atmospheres. The results suggest that deep-level defects originated by oxygen vacancy enhanced green emission, which reduce light transmittance and enhance the recombination of electrons in conduction band and holes in valence. More oxidizing environment is necessary to obtain defect-free ZnO film for higher transparency.
Park, Kyu Charn,Cha, Eun Seok,Shin, Dong Hyeop,Ahn, Byung Tae,Kwon, HyukSang Korea Photovoltaic Society 2014 Current Photovoltaic Research Vol.2 No.1
ZnSe/$Zn_3P_2$ heterojunctions with a substrate configuration were fabricated using a series of cost-effective processes. Thin films of ZnTe and $Zn_3P_2$ were successively grown by close-spaced sublimation onto Mo-coated glass substrates. ZnSe layers thinner than 100nm were formed by annealing the $Zn_3P_2$ films in selenium vapor. Surface selenization generated a high density of micro-cracks which, along with voids, provided shunt paths and severely deteriorated the diode characteristics. Annealing the $Zn_3P_2$ film at $300^{\circ}C$ in a $ZnCl_2$ atmosphere before surface selenization produced a dense microstructure and prevented micro-crack generation. The mechanism of micro-crack generation by the selenization was described and the suppression effect of $ZnCl_2$ treatment on the micro-crack generation was explained. ZnSe/$Zn_3P_2$ heterojunctions with low leakage current ($J_0$ < $1{\mu}A/cm^2$) were obtained using an optimized surface selenization process with $ZnCl_2$ treatment. However, the series resistance was very high due to the presence of an electrical barrier between the ZnTe and $Zn_3P_2$ layers.