F. Frühauf
Max Planck Society
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Publication
Featured researches published by F. Frühauf.
IEEE Journal of Photovoltaics | 2016
Otwin Breitenstein; F. Frühauf; Anthony Teal
When silicon solar cells are investigated by electro- or photoluminescence (PL) imaging using a silicon-based camera, photon scattering in the detector chip leads to a certain degree of blurring of the images, which can be removed by image deconvolution. The necessary point spread function (PSF) was originally measured directly by evaluating fine light spots, but this procedure needed the evaluation of several images. It was shown recently that evaluating an image with a sharp contrast edge in the middle may lead to a PSF spreading over longer distances by evaluating only one image. Here, we show that the previous backwards substitution method for obtaining this PSF does still lead to residual errors. An alternative method to derive the PSF from a measured contrast edge image is introduced here. It uses an iterative method, which leads to most precise results. In addition to the local deconvolution, nonlocal (homogeneous) light scattering is corrected. The correct reconstruction of the dark part of the image used for obtaining the PSF is a proof for the accuracy of this PSF.
IEEE Journal of Photovoltaics | 2016
Otwin Breitenstein; F. Frühauf; David Hinken; Karsten Bothe
Most methods for interpreting electroluminescence (EL) or photoluminescence (PL) images of solar cells evaluate the local diode voltages but not the local luminescence intensity itself. One exception is the Fuyuki approximation, which assumes that the local value of the luminescence signal is proportional to the local effective diffusion length. This dependence has been derived for infinitely thick solar cells and neglects self-absorption of the luminescence photons. However, for real solar cells and imaging conditions, with increasing diffusion length, the luminescence signal approaches a limiting value; hence, the Fuyuki approximation no longer holds. In this paper, we compare EL and PL images of multicrystalline solar cells using different kinds of light filtering and find that gentle shortpass filtering is useful for avoiding optical artifacts. Based on earlier calculations, a physically founded formula for the dependence of the gently shortpass-filtered luminescence signal on the bulk diffusion length, for a given rear surface recombination velocity, is presented. Since this formula only barely allows us to calculate the diffusion length from the luminescence signal, a simplified approximate formula is proposed, and its accuracy is checked. This method is tested on EL and Voc PL images of solar cells. We find that for a typical industrial multicrystalline Albackside solar cell, the obtained effective diffusion length images correlate well with such images obtained by spectral LBIC image evaluation. In addition, the saturation current density images correlate well with such images obtained by dark lock-in thermography, which show a much lower spatial resolution. The main limitation of the proposed method is that it is basically approximate and needs some fitting parameters.
Solar Energy Materials and Solar Cells | 2016
F. Frühauf; Otwin Breitenstein
Solar Energy Materials and Solar Cells | 2016
Otwin Breitenstein; F. Frühauf; M. Turek
Solar Energy Materials and Solar Cells | 2017
F. Frühauf; Johnson Wong; Jan S. Bauer; Otwin Breitenstein
Solar Energy Materials and Solar Cells | 2016
F. Frühauf; Yassine Sayad; Otto Breitenstein
Solar Energy Materials and Solar Cells | 2017
Jan S. Bauer; F. Frühauf; Otwin Breitenstein
Energy Procedia | 2016
Otwin Breitenstein; F. Frühauf; Jan S. Bauer; Florian Schindler; Bernhard Michl
Solar Energy Materials and Solar Cells | 2017
F. Frühauf; Otwin Breitenstein
Solar Energy Materials and Solar Cells | 2017
Otwin Breitenstein; F. Frühauf