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Analysis of Band Gap Fluctuations in Cu(In,Ga)Se2 by Confocal Optical Transmission and Photoluminescence

Published online by Cambridge University Press:  01 February 2011

Levent Gutay  and
Gottfried H. Bauer
Levent Gutay
Affiliation:
levent.guetay@uni-oldenburg.de, Carl von Ossietzky University Oldenburg, Institute of Physics, D-26111 Oldenburg, Oldenburg, 26111, Germany, +49 441 7983490, +49 441 7983201
Gottfried H. Bauer
Affiliation:
g.h.bauer@uni-oldenburg.de, Carl von Ossietzky University Oldenburg, Institute of Physics, Oldenburg, 26111, Germany
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Abstract

We present new insights into inhomogeneities of Cu(In,Ga)Se2 absorbers by confocal optical transmission (OT) and spectrally resolved photoluminescence (PL) with lateral resolution in the one-micron regime. We carry out scans for both measurands at identical positions and observe explicit local variations of the PL- and OT-spectra. The PL-yield shows fluctuations in the sub- and few-µm regime. As shown in previous papers we extract local variations of the splitting of quasi-Fermi-levels of about 40-50meV, which limits the open circuit voltage of cells, and of the optical threshold of the absorber of some tens of meV related to the local optical band gap. Local transmission spectra similarly show lateral variations in the few-µm regime. From these spectra we calculate local absorption coefficients and absorbance functions which yield variations of the optical threshold of the absorber of 20-30meV, amounting to the same range as PL-results. Via Planck's generalized law we are able to compute theoretical PL-spectra from the resulting absorbance functions. The discrepancies between measured and calculated hypothetical PL-spectra are discussed with respect to diffusion of excess charge carriers and fluctuations of the band gap in the sub-µm-regime below the spatial resolution of the experiment.

Keywords

optical propertiesoptoelectronicluminescence
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1012: Symposium Y – Thin-Film Compound Semiconductor Photovoltaics-2007 , 2007 , 1012-Y08-03
Copyright
Copyright © Materials Research Society 2007

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