Development of High-Efficiency Cd-Free Cu(In,Ga)Se2 Solar Cells Using Chemically Deposited ZnS Film
A ZnS film covered completely the CIGS surface without pinholes. The thickness of the ZnS film could be controlled according to the cycle number of the CBD process. As the thickness of the ZnS film increased, the JSC value of a CIGS solar cell with the ZnS film decreased sharply due to the increase in the series resistance of the cell. The QE spectrum of the CIGS solar cell with a 50 nm-thick ZnS film consequently showed very small values through the whole wavelength range. On the other hand, the VOC and FF values of the CIGS solar cell with a 27 nm-thick ZnS film were significantly influenced by the sputtering power for deposition of the ZnO:Al film. By decreasing the sputtering power during deposition of the ZnO:Al film, the VOC and FF values of the CIGS solar cells with a 27 nm-thick ZnS film were sharply improved due to a reduction of sputtering damage at the ZnS surface and ZnS/CIGS interface. Additionally, the JSC value of the CIGS solar cell with a 27 nm-thick ZnS film was improved by annealing the ZnS film. As a result of an annealing process, the QE value in a wavelength range of 400–700 nm increased. Finally, we achieved a conversion efficiency of 14.21 % for a CIGS solar cell with a ZnS film by optimizing the fabrication conditions.
KeywordsCu(In,Ga)se2 solar cell Zns buffer Chemical bath deposition
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This work was supported by the Center for Inorganic Photovoltaic Materials (No. 2012-0001167), the KAIST EEWS Initiative program (EEWS-2012-N00120013), and the Priority Research Center Program (2011-0031407) funded by the Korean Ministry of Education, Science and Technology.
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