Cu(In,Ga) Se2 (CIGS) thin film solar cells have demonstrated very high efficiencies, but still the role of nanoscale inhomogeneities in CIGS and their impact on the solar cell performance are not yet clearly understood. Due to the polycrystalline structure of CIGS, grain boundaries are very common structural defects that are also accompanied by compositional variations. In this work, we apply valence electron energy loss spectroscopy in scanning transmission electron microscopy to study the local band gap energy at a grain boundary in the CIGS absorber layer. Based on this example, we demonstrate the capabilities of a 2nd generation monochromator that provides a very high energy resolution and allows for directly relating the chemical composition and the band gap energy across the grain boundary. A band gap widening of about 20 meV is observed at the grain boundary. Furthermore, the compositional analysis by core-loss EELS reveals an enrichment of In together with a Cu, Ga and Se depletion at the same area. The experimentally obtained results can therefore be well explained by the presence of a valence band barrier at the grain boundary.
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10 October 2016
Research Article|
October 10 2016
Band gap widening at random CIGS grain boundary detected by valence electron energy loss spectroscopy
Debora Keller;
Debora Keller
a)
1Laboratory for Thin Films and Photovoltaics,
Empa - Swiss Federal Laboratories for Materials Science and Technology
, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
2Electron Microscopy Center,
Empa - Swiss Federal Laboratories for Materials Science and Technology
, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
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Stephan Buecheler;
Stephan Buecheler
1Laboratory for Thin Films and Photovoltaics,
Empa - Swiss Federal Laboratories for Materials Science and Technology
, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
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Patrick Reinhard;
Patrick Reinhard
1Laboratory for Thin Films and Photovoltaics,
Empa - Swiss Federal Laboratories for Materials Science and Technology
, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
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Fabian Pianezzi;
Fabian Pianezzi
1Laboratory for Thin Films and Photovoltaics,
Empa - Swiss Federal Laboratories for Materials Science and Technology
, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
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Benjamin Bissig;
Benjamin Bissig
1Laboratory for Thin Films and Photovoltaics,
Empa - Swiss Federal Laboratories for Materials Science and Technology
, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
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Romain Carron;
Romain Carron
1Laboratory for Thin Films and Photovoltaics,
Empa - Swiss Federal Laboratories for Materials Science and Technology
, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
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Fredrik Hage;
Fredrik Hage
3
SuperSTEM Laboratory
, SciTech Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, United Kingdom
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Quentin Ramasse;
Quentin Ramasse
3
SuperSTEM Laboratory
, SciTech Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, United Kingdom
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Rolf Erni;
Rolf Erni
2Electron Microscopy Center,
Empa - Swiss Federal Laboratories for Materials Science and Technology
, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
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Ayodhya N. Tiwari
Ayodhya N. Tiwari
1Laboratory for Thin Films and Photovoltaics,
Empa - Swiss Federal Laboratories for Materials Science and Technology
, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
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Appl. Phys. Lett. 109, 153103 (2016)
Article history
Received:
August 12 2016
Accepted:
September 27 2016
Citation
Debora Keller, Stephan Buecheler, Patrick Reinhard, Fabian Pianezzi, Benjamin Bissig, Romain Carron, Fredrik Hage, Quentin Ramasse, Rolf Erni, Ayodhya N. Tiwari; Band gap widening at random CIGS grain boundary detected by valence electron energy loss spectroscopy. Appl. Phys. Lett. 10 October 2016; 109 (15): 153103. https://doi.org/10.1063/1.4964516
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