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 Karl Franzens University Graz

Graz University of Technology 

Advanced transmission electron microscopy for the development of high‐efficiency solar cells
Prof. Dr. Wolfgang Jäger
Institute for Materials Science, Christian-Albrechts-University of Kiel
17:15 - 18:15 Tuesday 12 January 2016 TUG P2

Highly efficient multi-junction solar cells based on III-V compound semiconductor materials are applied for power generation in terrestrial concentration photovoltaics and in space applications. Solar-electric conversion efficiencies well above 40% have been obtained for concentrator solar cells grown by metal-organic vapor epitaxy on Ge cells. The high-resolution imaging and spectroscopic methods of transmission electron microscopy (TEM) can be applied successfully to supporting the development of novel solar cell concepts. Two application areas will be illustrated: concepts for buffer layer systems that control defects and layer strains in III-V dual-junction cells grown by metal organic vapor phase epitaxy on Ge and Si solar cells, and analyses of transparent and electrically conductive bond interfaces that are formed by direct wafer bonding of dual-junction solar cells grown on GaAs to separately fabricated Si solar cells. By applying aberration-corrected scanning TEM, combined with elemental analyses by electron-energy loss spectroscopy, the distributions of elements at the Ga/Si interfaces in wafer-bonded solar cells can be measured with high detection sensitivity, thus allowing to interpret the electrical properties of the direct wafer bond. Optimized solar cell concepts resulted in active cell regions with significantly reduced defect densities. The success of such concept developments led to a GaInP/GaAs//Ge cell with a record efficiency of 41.1 % and to a GaInP/GaAs//Si solar cell with a maximum efficiency of 30%. Current research aiming at higher solar cell efficiencies will be briefly addressed.

It is a pleasure to acknowledge the collaborations and the contributions of all colleagues mentioned in the references.

References
J. Schöne, E. Spiecker, F. Dimroth, A. W. Bett, W. Jäger: Misfit dislocation blocking by dilute nitride intermediate layers. Appl. Phys. Lett. 92, 081905 (2008).

J. Schöne, E. Spiecker, F. Dimroth, A. W. Bett, W. Jäger: Defect Formation and Strain Relaxation in Graded GaPAs/GaAs, GaNAs/GaAs and GaInNAs/Ge Buffer Systems for high-efficiency Solar Cells. Journal of Physics: Conference Series 471, 012008 (2013). DOI:10.1088/1742-6596/471/1/012008

K. Derendorf, S. Essig, E. Oliva, V. Klinger, T. Roesener, S.P. Philipps, J. Benick, M. Hermle, M. Schachtner, G. Siefer, W. Jäger, F. Dimroth, Fabrication of GaInP/GaAs//Si Solar Cells by Surface Activated Direct Wafer Bonding, IEEE Journal of Photovoltaics 3(4), 1423 - 1428 (2013)

D. Häussler, L. Houben, S. Essig, M. Kurttepeli, F. Dimroth, R. E. Duni-Borkowski, W. Jäger: Aberration-corrected transmission electron microscopy analyses of GaAs/Si interfaces in wafer-bonded multi-junction solar cells. Ultramicroscopy 134, 55–61 (2013).

F. Dimroth, T. Roesener, S. Essig, Ch. Weuffen, A. Wekkeli, E. Oliva, G. Siefer, K. Volz, Th. Hannappel, D. Häussler, W. Jäger, A. W. Bett: Comparison of Direct Growth and Wafer Bonding for the Fabrication of GaInP/GaAs Dual-Junction Solar Cells on Silicon. IEEE Journal of Photovoltaics 4 (2), 620-625 (2014).

S. Essig, J. Benick, M. Schachtner, A. Wekkeli, M. Hermle, F. Dimroth: Wafer-Bonded GaInP/GaAs//Si Solar Cells With 30% Efficiency under Concentrated Sunlight. IEEE Journal of Photovoltaics 5 (3), 977-981 (2015).