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- Igalson, M., et al.
(författare)
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Concentration of defects responsible for persistent photoconductivity in Cu (In,Ga)Se-2 : Dependence on material composition
- 2019
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 669, s. 600-604
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Tidskriftsartikel (refereegranskat)abstract
- Persistent photoconductivity (PPC) in thin Cu(In,Ga)Se-2 films is discussed within a model of relaxing defects acting as donors or acceptors depending on their configurational and charge state. The aim of this work is to identify the factors related to technological processes which affect the magnitude of PPC. We established a method of evaluation of the concentration of metastable defects in thin Cu(In,Ga)Se-2 films relating it to the position of the Fermi level in thermodynamic equilibrium and used it to compare and discuss the impact of preparation details on the PPC value. The main result is that deviation from Cu/(Ga + In) stoichiometry does not change the concentration of metastable defects. Post deposition annealing in selenium affects the PPC depending on the presence of sodium during the treatment, while the impact of sodium itself on the metastable defect concentration apparently depends on whether it is present during the Cu(In,Ga)Se-2 deposition process or whether it is supplied during post-deposition treatment.
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| 2. |
- Igalson, M., et al.
(författare)
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Metastabilities in the electrical characteristics of CIGS devices : Experimental results vs theoretical predictions
- 2007
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:15, s. 6142-6146
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Tidskriftsartikel (refereegranskat)abstract
- Recent theoretical calculations have traced an origin of light- and voltage bias-induced metastabilities in Cu(In,Ga)Se2-based solar cells to negative-U properties of the VSe–VCu complex. In this paper we compare experimental findings with theoretically predicted properties of these defects and calculated values of parameters characteristic for transitions between their different states. Profiles of net acceptor concentrations in the relaxed and metastable states obtained by capacitance profiling have been studied, as well as annealing kinetics of the persistent defect distributions by thermally stimulated capacitance and conductivity. Good qualitative and quantitative agreement are found between theory of VSe-related defects and experimental results. The consequences from the point of view of photovoltaic efficiency of the Cu(In,Ga)Se2-based solar cells are discussed.
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| 7. |
- Igalson, M., et al.
(författare)
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Excitation spectra of defect levels derived from photoinduced current transient spectroscopy - a tool for studying deep levels in Cu(In,Ga)Se2 compounds
- 2017
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 633:SI, s. 227-230
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Tidskriftsartikel (refereegranskat)abstract
- Energy required for the optical excitation of carriers onto defect levels is a parameter that compliments thermal activation energy and helps to understand the electronic properties of defects under study. Here a modification of the photoinduced current transient spectroscopy (PICTS) based on phase-sensitive detection is proposed which makes possible to measure the excitation spectra of defect levels. The representative results of the excitation spectra of the epitaxial CuGaSe2 and polycrystalline Cu(In,Ga)Se2 thin films are presented. They illustrate the usefulness of the method as a tool for studying defect properties by providing data that supplement information derived from standard PICTS spectroscopy.
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| 8. |
- Igalson, M., et al.
(författare)
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Metastable Defect Distributions and Spectral Photoresponse of CIGS Devices
- 2010
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Konferensbidrag (refereegranskat)abstract
- Metastable changes of photovoltaic parameters in baseline CIGS devices are investigated. In order to gain more insight into origin of these changes induced in particular by the reverse bias stress, quantum efficiency distribution together with current-voltage chracteristics are investigated with and without presence of blue illumination absorbed in CdS buffer. We show that photocurrent is affected by two barriers: one located in the absorber and related to the p+ layer enhanced by reverse bias treatment under elevated temperatures, and second related to negative charge accumulated most probably at CdS/i-ZnO interface. While the second barrier causes severe fill factor losses only under red illumination but is easily reduced by blue photons present in white light, the first one impedes current transport also under full spectrum. The results and simulations performed by using SCAPS software show the relation between both barriers: the more charge is accumulated in the p+ layer the more detrimental is the effect of the second barrier.
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