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Stuttgart Mühlhausen, Germany

Li-Kao Z.J.,Chimie Paristech | Naghavi N.,Chimie Paristech | Erfurth F.,Chimie Paristech | Guillemoles J.F.,Chimie Paristech | And 6 more authors.
Progress in Photovoltaics: Research and Applications | Year: 2012

An innovative approach combining chemical etching and a "lift-off" process, which allows back contact processing after CIGSe deposition, permitted to use Au as a highly reflective back contact in ultrathin CIGSe solar cells. The Au back contact does not degrade the other parameters of the cell, as good ohmicity on CIGSe is achieved. An important photocurrent increase compared with regular Mo back contact solar cells is achieved by the enhanced light trapping effect due to the back reflector, leading to an absolute efficiency increase of +2.5% for a CIGSe thickness of 0.4 μm. This approach could be used for further investigations in improving the back side of ultrathin CIGSe solar cells. Copyright © 2012 John Wiley & Sons, Ltd.

Jehl Z.,Ecole Nationale Superieure de Chimie de Paris | Erfurth F.,Ecole Nationale Superieure de Chimie de Paris | Naghavi N.,Ecole Nationale Superieure de Chimie de Paris | Lombez L.,Ecole Nationale Superieure de Chimie de Paris | And 10 more authors.
Thin Solid Films | Year: 2011

In this paper, the influence of reducing the thickness of the CIGSe absorber layer by bromine etching from 2.5 μm to 0.5 μm on electrical and optical solar cell properties is addressed. We observe a decrease in efficiency which is mainly caused by a reduced short circuit current, whereas the fill factor and the open circuit voltage are stable. Even without deliberate light trapping or anti-reflection coating, an efficiency of 10.3% is obtained for a 0.5 μm thick CIGSe absorber. A smoothing of the absorber surface is observed during the etching, its influence on the cell parameters will be discussed. © 2011 Elsevier B.V.

Bouttemy M.,French National Center for Scientific Research | Tran-Van P.,French National Center for Scientific Research | Gerard I.,French National Center for Scientific Research | Hildebrandt T.,French National Center for Scientific Research | And 11 more authors.
Thin Solid Films | Year: 2011

CIGSe absorber was etched in HBr/Br2/H2O to prepare defined thicknesses of CIGSe between 2.7 and 0.5 μm. We established a reproducible method of reducing the absorber thickness via chemical etching. We determine the dissolution kinetics rate of CIGSe using trace analysis by graphite furnace atomic absorption spectrometry of Ga and Cu. The roughness of the etching surface decreases during the first 500 nm of the etching to a steady state value of the root-mean-square roughness near 50 nm. X-ray photoelectron spectroscopy analyses demonstrate an etching process occurring with a constant chemical composition of the treated surface acidic bromine solutions provide a controlled chemical thinning process resulting in an almost flat surface and a very low superficial Se0 enrichment. © 2011 Elsevier B.V.

Erfurth F.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep | Jehl Z.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep | Bouttemy M.,University of Versailles | Dahan N.,Ecole Polytechnique - Palaiseau | And 9 more authors.
Applied Surface Science | Year: 2012

Chemical and optical properties of the interface between a coevaporated Cu(In,Ga)Se 2 (CIGSe) absorber thin film and the Mo back contact are investigated with the objective to reduce markedly the thickness of CIGSe layers from two microns down to about 100 nm. First a mechanical lift off technique allowed to separate Mo and CIGSe layers and perform X-ray photoelectron spectroscopy (XPS) and elipsometry studies on as prepared surfaces. On the Mo side small amounts of In and Ga are observed together with the formation of an MoSe 2 layer. There is no evidence of the presence of Cu. On the opposite CIGSe side a clear depletion of Cu together with an enrichment of Ga is evidenced. There is no evidence of Mo. Optical reflectivity of the interface CIGSe/Mo is studied by ellipsometry showing a low reflectivity of the interface attributed to the formation of MoSe 2 layer. The enhance light absorption in ultrathin absorbers using alternative, highly reflective back contacts are finally discussed. © 2011 Elsevier B.V. All rights reserved.

Jehl Z.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique | Bouttemy M.,University of Versailles | Lincot D.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique | Guillemoles J.F.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique | And 5 more authors.
Journal of Applied Physics | Year: 2012

The influence of Cu(In,Ga)Se 2 (CIGSe) surface roughness on the photovoltaic parameters of state of the art devices is reported, highlighting the importance of the roughness of the as-grown CIGSe absorbers on solar cell efficiencies. As-grown CIGSe surface is progressively smoothed using a chemical etch, and characterized by SEM, AFM, XPS, μ-Raman spectroscopy, x-ray diffraction (XRD), and reflectivity. The decrease of roughness has no marked influence on crystal structure and surface composition of the absorber. The main effect is that the total reflectivity of the CIGSe surface increases with decreasing roughness. The samples are processed into solar cells and characterized by current-voltage measurements. While the open circuit voltage (V oc) and fill factor remain constant, the short circuit current (J sc) decreases markedly with decreasing roughness, resulting in a reduction of the solar cell efficiency from 14 down to 11, which exceeds the expected decrease from increased reflectivity. Quantum efficiency and reflectivity measurements on complete cells are performed to analyze those effects. The influence of surface roughness on the theorical effective space charge region and diffusion length is based on a simple theoretical model. This paper discusses the comparison of CIGSe solar cells with n-i-p structures. © 2012 American Institute of Physics.

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