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ABSTRACT: In this work, we studied the impact of using Zn<sub>1-x</sub>Mg<sub>x</sub>O to replace the intrinsic ZnO in CIGS solar cells. The effect of Mg content and layer thickness of the Zn<sub>1-x</sub>Mg<sub>x</sub>O on device formation was investigated. We found that the amount of Mg in the Zn<sub>1-x</sub>Mg<sub>x</sub>O layer and the layer thickness significantly alter the cell properties. Device characterization indicated that the impact of the Mg content is not limited to the front-window layer, but also extends to underneath the CIGS layer. The numerical simulation nicely explains the relationship between various front-window layers and device performance. Our observation indicates that properties of the front-window layer may be important to junction formation in CIGS devices. Any changes to this part of the device could seriously alter device performance.
Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE; 07/2009
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ABSTRACT: The authors have fabricated 19.52% thin-film CuIn1−xGaxSe2 (CIGS)-based photovoltaic devices using single layer chemical bath deposited Cd1−xZnxS (CdZnS) buffer layer. The efficiency equals the world record for any thin-film solar cell and is achieved with reduced optical absorption in the window layer. Using current-voltage, quantum efficiency, and capacitance-voltage measurements, the CIGS/CdZnS device parameters are directly compared with those of CIGS/CdS devices fabricated with equivalent absorbers.
Applied Physics Letters 12/2006; 89(25):253503-253503-2. · 3.84 Impact Factor
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ABSTRACT: We report a new state of the art in thin-film polycrystalline Cu(In,Ga)Se2-based solar cells with the attainment of energy conversion efficiencies of 19·5%. An analysis of the performance of Cu(In,Ga)Se2 solar cells in terms of some absorber properties and other derived diode parameters is presented. The analysis reveals that the highest-performance cells can be associated with absorber bandgap values of ∼1·14 eV, resulting in devices with the lowest values of diode saturation current density (∼3×10−8 mA/cm2) and diode quality factors in the range 1·30 < A < 1·35. The data presented also support arguments of a reduced space charge region recombination as the reason for the improvement in the performance of such devices. In addition, a discussion is presented regarding the dependence of performance on energy bandgap, with an emphasis on wide-bandgap Cu(In,Ga)Se2 materials and views toward improving efficiency to > 1;20% in thin-film polycrystalline Cu(In,Ga)Se2 solar cells. Published in 2005 John Wiley & Sons, Ltd.
Progress in Photovoltaics Research and Applications 04/2005; 13(3):209 - 216. · 5.79 Impact Factor
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ABSTRACT: The growth and characterization of Cu(In,Ga)Se 2 polycrystalline thin films under the presence of thin-MF (M=Na, K, Cs) precursor layers is presented. Some electrical, structural, and electronic absorber properties due to the presence of such Group Ia impurities are quantified along with their influence in device performance. We present a growth model for the role of Na in Cu(In,Ga)Se 2 that attributes the enhancements in electrical conductivity and photovoltaic device performance to the extinction of a finite number of donor states (i.e., In Cu ) at the bulk and grain-boundary regions.
10/1998;
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ABSTRACT: The growth and characterization of Cu(In,Ga)Se<sub>2</sub>
polycrystalline thin film solar cells under the presence of thin-MF
(M=Na, K, Cs) precursor layers is presented. Some electrical, structural
and electronic absorber properties due to the presence of such Group Ia
impurities are quantified along with their influence in device
performance. The authors present a growth model for the role of Na in
Cu(In,Ga)Se<sub>2</sub> that attributes the enhancements in electrical
conductivity and photovoltaic device performance to the extinction of a
finite number of donor states (i.e., In<sub>Cu</sub>) at the bulk and
grain-boundary regions
Photovoltaic Specialists Conference, 1997., Conference Record of the Twenty-Sixth IEEE;
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ABSTRACT: We present temperature-dependent hole drift mobility measurements on polycrystalline CuIn1−xGaxSe2 (CIGS) thin films incorporated into solar-cell structures. The drift mobilities were determined from photocarrier time-of-flight measurements in a depletion region at the top interface with cadmium sulfide. 12 cells, originating in two laboratories, were examined. The drift mobilities ranged from 0.02 to 0.7 cm2/Vs at room temperature and were weakly temperature dependent in the range of 100–300 K. These drift mobilities are at the low end of the range of hole mobilities reported from previous Hall effect and admittance measurements for varying CIGS materials. We found approximately a square-root correlation between the width of the depletion layer in our samples and the magnitude of the drift mobility. Both the magnitude and the temperature dependence of the drift mobility are consistent with results in amorphous and nanocrystalline silicon that have been modeled using a disorder-induced transport edge. The source of nanometer-scale disorder in these CIGS materials is not noncrystallinity; chemical composition fluctuations are one alternative source of disorder. The correlation of the depletion-width and drift mobility measurements in CIGS may be evidence for a broader effect of disorder in these materials in both reducing the carrier drift mobility and generating acceptor defects near the valence bandedge. Hole drift mobilities are sensitive to disorder-induced traps near the valence bandedge. Our temperature-dependence measurements indicate that the width of the corresponding valence bandtail is less than 20 meV. Previous optical-absorption spectroscopy showed that Urbach tails in similar CIGS samples are generally 20 meV or wider, which indicates that the valence bandtail does not typically determine the Urbach tails.
Phys. Rev. B. 80(23).
