A CdS buffer layer is commonly used for high efficiency Cu(In,Ga)Se2 (CIGS) solar cells, and is typically prepared by chemical bath deposition (CBD) method. However, Cd has several disadvantages such as toxic material and less response of short wavelength than other materials due to the low band gap...
A CdS buffer layer is commonly used for high efficiency Cu(In,Ga)Se2 (CIGS) solar cells, and is typically prepared by chemical bath deposition (CBD) method. However, Cd has several disadvantages such as toxic material and less response of short wavelength than other materials due to the low band gap of 2.4 ~ 2.5 eV. From the viewpoint of the need for in-line processing for mass production, there is a need to find an alternative to wet-chemically deposited CdS. Herein, we choose the ZnS film as a buffer layer, which was prepared by a DC sputtering of Zn, followed by the subsequent sulfurization by S cracker. The notable thing is the use of sulfur thermal cracker cell for formation of ZnS film which is deposited by varying cracking zone temperature. To investigate physical and electrical properties, the cracker-ZnS films depending on cracking zone temperature were characterized by X-ray diffraction, Rutherford backscattering spectroscopy, Scanning electron microscopy, and Uv-Vis spectroscopy. Next, another issue is the selection of window layer in CIGS solar cell. An intrinsic zinc oxide (i-ZnO) and indium-tin-oxide (ITO) thin film as window layers are widely used in a CIGS solar cell and are typically deposited by using RF magnetron sputtering. However, the photovoltaic performance was found to degrade with the RF magnetron sputtering of i-ZnO, which was related to the plasma damage to the buffer/CIGS layer. To investigate the relationship of solar performance degradation to the underlying film quality, we varied the RF sputtering power of i-ZnO from 100 W to 400 W. We discuss two effects as the cause of solar cell degradation; one is the change of physical properties of i-ZnO thin film and the other is the plasma damage induced by RF sputtering on the ZnS/CIGS layer. To evaluate the plasma damage, we prepared i-ZnO films on a GaAs substrate by RF-sputtering and investigated the difference of electrical conductivity of a GaAs substrate after removing i-ZnO films by a 4-point probe. In addition, the physical and optical properties of i-ZnO thin film were characterized by using an X-ray diffraction, a scanning electron microscopy, and UV-VIS spectrometer. In this experiment, the CIGS solar cells were fabricated with a cracker-ZnS buffer layer on CIGS absorber and RF sputter-grown i-ZnO and ITO window layer. In the current-voltage measurement of the CIGS solar cell, we obtained the best performance of Jsc = 37.40 mA/cm2, Voc = 0.504 V, FF = 66.80, and η = 12.60 % for the sample with ZnS film formed at cracking temperature of 700 ℃ and i-ZnO film deposited at the RF power of 100 W.
A CdS buffer layer is commonly used for high efficiency Cu(In,Ga)Se2 (CIGS) solar cells, and is typically prepared by chemical bath deposition (CBD) method. However, Cd has several disadvantages such as toxic material and less response of short wavelength than other materials due to the low band gap of 2.4 ~ 2.5 eV. From the viewpoint of the need for in-line processing for mass production, there is a need to find an alternative to wet-chemically deposited CdS. Herein, we choose the ZnS film as a buffer layer, which was prepared by a DC sputtering of Zn, followed by the subsequent sulfurization by S cracker. The notable thing is the use of sulfur thermal cracker cell for formation of ZnS film which is deposited by varying cracking zone temperature. To investigate physical and electrical properties, the cracker-ZnS films depending on cracking zone temperature were characterized by X-ray diffraction, Rutherford backscattering spectroscopy, Scanning electron microscopy, and Uv-Vis spectroscopy. Next, another issue is the selection of window layer in CIGS solar cell. An intrinsic zinc oxide (i-ZnO) and indium-tin-oxide (ITO) thin film as window layers are widely used in a CIGS solar cell and are typically deposited by using RF magnetron sputtering. However, the photovoltaic performance was found to degrade with the RF magnetron sputtering of i-ZnO, which was related to the plasma damage to the buffer/CIGS layer. To investigate the relationship of solar performance degradation to the underlying film quality, we varied the RF sputtering power of i-ZnO from 100 W to 400 W. We discuss two effects as the cause of solar cell degradation; one is the change of physical properties of i-ZnO thin film and the other is the plasma damage induced by RF sputtering on the ZnS/CIGS layer. To evaluate the plasma damage, we prepared i-ZnO films on a GaAs substrate by RF-sputtering and investigated the difference of electrical conductivity of a GaAs substrate after removing i-ZnO films by a 4-point probe. In addition, the physical and optical properties of i-ZnO thin film were characterized by using an X-ray diffraction, a scanning electron microscopy, and UV-VIS spectrometer. In this experiment, the CIGS solar cells were fabricated with a cracker-ZnS buffer layer on CIGS absorber and RF sputter-grown i-ZnO and ITO window layer. In the current-voltage measurement of the CIGS solar cell, we obtained the best performance of Jsc = 37.40 mA/cm2, Voc = 0.504 V, FF = 66.80, and η = 12.60 % for the sample with ZnS film formed at cracking temperature of 700 ℃ and i-ZnO film deposited at the RF power of 100 W.
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