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Gallium gradients in Cu(In,Ga)Se2 thin-film solar cells

Witte, Wolfram and Abou-Ras, Daniel and Albe, Karsten and Bauer, Gottfried H. and Bertram, Frank and Boit, Christian and Brüggemann, Rudolf and Christen, Jürgen and Dietrich, Jens and Eicke, Axel and Hariskos, Dimitrios and Maiberg, Matthias and Mainz, Roland and Meessen, Max and Müller, Mathias and Neumann, Oliver and Orgis, Thomas and Paetel, Stefan and Pohl, Johan and Rodriguez-Alvarez, Humberto and Scheer, Roland and Schock, Hans-Werner and Unold, Thomas and Weber, Alfons and Powalla, Michael (2015):
Gallium gradients in Cu(In,Ga)Se2 thin-film solar cells.
In: Progress in Photovoltaics: Research and Applications, John Wiley & Sons, Ltd, pp. 717-733, 23, ISSN 10627995,
[Online-Edition: http://dx.doi.org/10.1002/pip.2485],
[Article]

Abstract

The gallium gradient in Cu(In,Ga)Se2 (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co-evaporation processes, plays a key role in the device performance of CIGS thin-film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X-ray measurements. In addition, the gallium grading of a CIGS layer grown with an in-line coevaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth-dependent occurrence of lateral inhomogeneities on the μm scale in CIGS deposited by the co-evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi-Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross-sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper-vacancy-mediated indium and gallium diffusion in CuInSe2 and CuGaSe2 were calculated using density functional theory. The migration barrier for the InCu antisite in CuGaSe2 is significantly lower compared with the GaCu antisite in CuInSe2, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co-evaporation and selenization processes.

Item Type: Article
Erschienen: 2015
Creators: Witte, Wolfram and Abou-Ras, Daniel and Albe, Karsten and Bauer, Gottfried H. and Bertram, Frank and Boit, Christian and Brüggemann, Rudolf and Christen, Jürgen and Dietrich, Jens and Eicke, Axel and Hariskos, Dimitrios and Maiberg, Matthias and Mainz, Roland and Meessen, Max and Müller, Mathias and Neumann, Oliver and Orgis, Thomas and Paetel, Stefan and Pohl, Johan and Rodriguez-Alvarez, Humberto and Scheer, Roland and Schock, Hans-Werner and Unold, Thomas and Weber, Alfons and Powalla, Michael
Title: Gallium gradients in Cu(In,Ga)Se2 thin-film solar cells
Language: English
Abstract:

The gallium gradient in Cu(In,Ga)Se2 (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co-evaporation processes, plays a key role in the device performance of CIGS thin-film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X-ray measurements. In addition, the gallium grading of a CIGS layer grown with an in-line coevaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth-dependent occurrence of lateral inhomogeneities on the μm scale in CIGS deposited by the co-evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi-Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross-sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper-vacancy-mediated indium and gallium diffusion in CuInSe2 and CuGaSe2 were calculated using density functional theory. The migration barrier for the InCu antisite in CuGaSe2 is significantly lower compared with the GaCu antisite in CuInSe2, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co-evaporation and selenization processes.

Journal or Publication Title: Progress in Photovoltaics: Research and Applications
Volume: 23
Publisher: John Wiley & Sons, Ltd
Uncontrolled Keywords: Cu(In,Ga)Se2, selenization, co-evaporation, gallium gradient, inhomogeneity, simulation
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 13 May 2014 08:41
Official URL: http://dx.doi.org/10.1002/pip.2485
Identification Number: doi:10.1002/pip.2485
Related URLs:
Funders: This work was funded by the German Federal Ministry of Education and Research (BMBF) under contract number 03SF0359 (GRACIS)., The support of the EDDI beamline team and CIGS baseline team at HZB is gratefully acknowledged.
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