Reference : Photoluminescence and solar cell studies of chalcopyrites - comparison of Cu-rich vs....
Dissertations and theses : Doctoral thesis
Physical, chemical, mathematical & earth Sciences : Physics
Photoluminescence and solar cell studies of chalcopyrites - comparison of Cu-rich vs. Cu-poor and polycrystalline vs. epitaxial material
Regesch, David mailto [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit >]
University of Luxembourg, ​​Luxembourg
Docteur en Physique
Siebentritt, Susanne mailto
[en] CuInSe2 ; photoluminescence ; epitaxy ; Urbach energy ; band gap ; quasi-Fermi level splitting ; solar cell ; Cu(In,Ga)Se2
[en] The quasi-Fermi level splitting (qFls) in a solar cell absorber limits the maximum achievable open circuit voltage of the final device. A calibrated photoluminescence set-up allows the determination of the qFls at room temperature under conditions equivalent to the illumination from the sun. In this work the qFls is used as an indicator for the quality of epitaxial and polycrystalline thin CuInSe2 films with different compositions.
It is shown, that the epitaxial material exhibits improved optoelectronic quality noticeable in the higher qFls (50-100meV) when compared to the polycrystalline counterpart. Furthermore, a dependency on the Cu/In ratio is noticed: In Cu poor material (Cu/In<1) the qFls increases with an increasing Cu concentration and levels off for the absorbers grown under Cu-rich conditions (Cu/In>1). The difference between absorbers grown under Cu-poor and Cu-rich conditions is found to be in the order of 150meV. Additionally, the compositional dependence of the Urbach energy and of the band gap energy has been evaluated from the PL spectra at room temperature. Slightly higher bandgaps and lower Urbach energies have been found for the Cu rich material compared to the Cu poor absorbers.
The time dependent change of the qFls of bare CuInSe2 absorbers exposed to air is presented and shows for Cu-poor absorbers a pronounced and for Cu-rich material a slower degradation. It is shown, that a chemical etching in potassium cyanide refreshes the degraded material to an extent comparable to freshly grown samples, and that the deposition of a CdS buffer layer passivates the surface.
Epitaxial Cu(In,Ga)Se2 is grown by means of metal organic vapour phase epitaxy and used to produce epitaxial solar cells. A maximum power conversion efficiency of 6.7% has been achieved. All solar cells suffer from dominant interface recombination processes which limit the device performance. The critical interface is between the absorber layer and the CdS buffer and related to the high gallium content.
Fonds National de la Recherche - FnR
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