ABSTRACT The defect levels in epitaxial and polycrystalline wide bandgap chalcopyrite CuGaSe2 wit... more ABSTRACT The defect levels in epitaxial and polycrystalline wide bandgap chalcopyrite CuGaSe2 with various stoichiometry deviations were investigated using modulated photocurrent spectroscopy. The results were analyzed as a function of light intensity and Fermi-level position. Comparison of the results from epitaxial and polycrystalline material distinguished levels belonging to intrinsic defects and their correlation with the material stoichiometry. We also compared the fingerprints of defect levels by MPC to the results derived from capacitance spectroscopy performed on Schottky diodes fabricated on both epitaxial and polycrystalline layers. This allowed us to attribute unambiguously levels observed in the capacitance response to bulk point defects. In the final conclusions we provide information on the electronic parameters of nine defect levels observed in CuGaSe2 and their correlation with the material stoichiometry. These results should help to identify intrinsic defects that are important for the photovoltaic performance of solar cells based on chalcopyrites.
ABSTRACT The compositional dependence of the optoelectronic quality of CuInSe2 thin film absorber... more ABSTRACT The compositional dependence of the optoelectronic quality of CuInSe2 thin film absorbers is investigated on single- and poly-crystalline films with varying [Cu]/[In]-ratios. We quantify the quality of the absorbers by the splitting of quasi-Fermi levels, determined by spectral photoluminescence. This quantity determines the maximum achievable open circuit voltage by an absorber. Our results indicate a significant increase of this value for growth under Cu-excess, indicating a decrease of recombination losses. By comparison of the predicted achievable open circuit voltage and the actually measured ones of finished solar cells, we find a huge “un-utilized potential” for the Cu-rich devices.
ABSTRACT The degradation of CuInSe2 absorbers in ambient air is observed by the decay of the quas... more ABSTRACT The degradation of CuInSe2 absorbers in ambient air is observed by the decay of the quasi-Fermi level splitting under well defined illumination with time. The decay is faster and stronger in absorbers with [Cu]/[In]<1 than in ones with a higher ratio. It can be attributed to the oxidation of the sample. Epitaxial films containing no Na show very similar trends, indicating that decay and oxidation are independent of the Na content. A standard CdS layer commonly used as buffer in solar cells, terminates the decay even over many months. Aged absorbers can be completely restored by a KCN etch.
... 139(1), 144 (1998). 13G. Moh, Chemie der Erde 34, 1 (1975). 14H. Hahn and H. Schulze, Naturwi... more ... 139(1), 144 (1998). 13G. Moh, Chemie der Erde 34, 1 (1975). 14H. Hahn and H. Schulze, Naturwiss. 52, 426 (1965). 15A. ... 151(1), 84–86 (2011). 19A.-J. Cheng, M. Manno, A. Khare, C. Leighton, SA Campbell, and ES Aydil, J. Vac. Sci. Technol. A 29(5), 051203 (2011). ...
ABSTRACT Epitaxial thin film CuGaSe2 and CuInSe2 samples grown on GaAs substrates with varying [C... more ABSTRACT Epitaxial thin film CuGaSe2 and CuInSe2 samples grown on GaAs substrates with varying [Cu]/[Ga,In] ratios were studied using positron annihilation Doppler-broadening spectroscopy and were compared to bulk crystals. We find both Cu monovacancies and Cu-Se divacancies in CuInSe2, whereas, in CuGaSe2, the only observed vacancy defect is the Cu-Se divacancy.
ABSTRACT The defect levels in epitaxial and polycrystalline wide bandgap chalcopyrite CuGaSe2 wit... more ABSTRACT The defect levels in epitaxial and polycrystalline wide bandgap chalcopyrite CuGaSe2 with various stoichiometry deviations were investigated using modulated photocurrent spectroscopy. The results were analyzed as a function of light intensity and Fermi-level position. Comparison of the results from epitaxial and polycrystalline material distinguished levels belonging to intrinsic defects and their correlation with the material stoichiometry. We also compared the fingerprints of defect levels by MPC to the results derived from capacitance spectroscopy performed on Schottky diodes fabricated on both epitaxial and polycrystalline layers. This allowed us to attribute unambiguously levels observed in the capacitance response to bulk point defects. In the final conclusions we provide information on the electronic parameters of nine defect levels observed in CuGaSe2 and their correlation with the material stoichiometry. These results should help to identify intrinsic defects that are important for the photovoltaic performance of solar cells based on chalcopyrites.
ABSTRACT The compositional dependence of the optoelectronic quality of CuInSe2 thin film absorber... more ABSTRACT The compositional dependence of the optoelectronic quality of CuInSe2 thin film absorbers is investigated on single- and poly-crystalline films with varying [Cu]/[In]-ratios. We quantify the quality of the absorbers by the splitting of quasi-Fermi levels, determined by spectral photoluminescence. This quantity determines the maximum achievable open circuit voltage by an absorber. Our results indicate a significant increase of this value for growth under Cu-excess, indicating a decrease of recombination losses. By comparison of the predicted achievable open circuit voltage and the actually measured ones of finished solar cells, we find a huge “un-utilized potential” for the Cu-rich devices.
ABSTRACT The degradation of CuInSe2 absorbers in ambient air is observed by the decay of the quas... more ABSTRACT The degradation of CuInSe2 absorbers in ambient air is observed by the decay of the quasi-Fermi level splitting under well defined illumination with time. The decay is faster and stronger in absorbers with [Cu]/[In]<1 than in ones with a higher ratio. It can be attributed to the oxidation of the sample. Epitaxial films containing no Na show very similar trends, indicating that decay and oxidation are independent of the Na content. A standard CdS layer commonly used as buffer in solar cells, terminates the decay even over many months. Aged absorbers can be completely restored by a KCN etch.
... 139(1), 144 (1998). 13G. Moh, Chemie der Erde 34, 1 (1975). 14H. Hahn and H. Schulze, Naturwi... more ... 139(1), 144 (1998). 13G. Moh, Chemie der Erde 34, 1 (1975). 14H. Hahn and H. Schulze, Naturwiss. 52, 426 (1965). 15A. ... 151(1), 84–86 (2011). 19A.-J. Cheng, M. Manno, A. Khare, C. Leighton, SA Campbell, and ES Aydil, J. Vac. Sci. Technol. A 29(5), 051203 (2011). ...
ABSTRACT Epitaxial thin film CuGaSe2 and CuInSe2 samples grown on GaAs substrates with varying [C... more ABSTRACT Epitaxial thin film CuGaSe2 and CuInSe2 samples grown on GaAs substrates with varying [Cu]/[Ga,In] ratios were studied using positron annihilation Doppler-broadening spectroscopy and were compared to bulk crystals. We find both Cu monovacancies and Cu-Se divacancies in CuInSe2, whereas, in CuGaSe2, the only observed vacancy defect is the Cu-Se divacancy.
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Papers by Levent Gütay