Band gap widening at random CIGS grain boundary detected by valence electron energy loss spectroscopy

Keller, D., Buecheler, S., Reinhard, P., Pianezzi, F., Bissig, B., Carron, R., Hage, F., Ramasse, Q., Erni, R. and Tiwari, A. N. (2016) Band gap widening at random CIGS grain boundary detected by valence electron energy loss spectroscopy. Applied Physics Letters, 109(15), 153103. (doi: 10.1063/1.4964516)

Abstract

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.

• Item Type: Articles
• Additional Information: The financial support from the Swiss National Science Foundation (SNF) (Project No. 200020_132377) and the UK National Facility for Aberration-Corrected STEM, supported by the Engineering and Physical Scences Research Council (EPSRC), are greatly acknowledged.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Hage, Dr Fredrik Sydow
• Authors: Keller, D., Buecheler, S., Reinhard, P., Pianezzi, F., Bissig, B., Carron, R., Hage, F., Ramasse, Q., Erni, R., and Tiwari, A. N.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Applied Physics Letters
• Publisher: AIP Publishing
• ISSN: 0003-6951
• ISSN (Online): 1077-3118
• Copyright Holders: Copyright © 2016 The Authors
• First Published: First published in Applied Physics Letters 109(15): 153103
• Publisher Policy: Reproduced in accordance with the publisher copyright policy