Technical Publications
Overview Papers
T. Trupke et al., “Progress with luminescence imaging for the characterisation of silicon wafers and solar cells” Invited plenary presentation at the 22nd EPVSC, Milan, Italy, 2007.
T. Trupke and R.A. Bardos, “ Photoluminescence: A versatile charaterisation technique for crystalline Silicon”, 15th Crystalline Silicon Workshop, Vail, USA, August 2005.
Background
P. Würfel, „The chemical potential of radiation“, J.Phys.C. 15, (1982) 3967.
The generalized Planck equation is derived, a quantitative relationship between the luminescence spectrum the separation of the quasi-Fermi Energies, the photon chemical potential and the absorption coefficient. This relationship is the basis for the theoretical analysis of the luminescence emission spectrum in terms of optical material- and sample parameters
E. Daub and P. Würfel, “Ultralow values of the absorption coefficient of Si obtained from luminescence”, Physical Review Letters 74(6) (1995) 1020-1023.
Example for the application of the generalized Planck equation to photoluminescence measurements on crystalline silicon wafers. The experimental results are analysed to determine extremely low values of the absorption coefficient for band-band transitions from the luminescence spectra.
T. Trupke, E. Daub, and P. Würfel, “Absorptivity of silicon solar cells obtained from luminescence”, Solar Energy Materials and Solar Cells 53(1-2) (1998) 103-114[1].
The generalized Planck equation is used to derive a quantitative relationship between the luminescence spectrum and the spectral absorptance of a solar cell. It is shown that the enhanced light trapping properties of textured wafers are reflected in the emission spectrum exactly as theoretically predicted. It is also shown that on high quality solar cells a quantitative value for the average path length enhancement achieved via texturing can be obtained.
Photoluminescence Lifetime Measurements (QSS-PL)
T. Trupke, R.A. Bardos, F. Hudert, P. Würfel, A. Wang, J. Zhao, and M.A. Green, “Effective excess minority carrier lifetimes exceeding 100 milliseconds in float zone silicon determined from photoluminescence”, 19th EPVSC, Paris, France (2004).
First experimental demonstration of quasi steady state photoluminescence (QSS-PL) measurements as an experimental technique to measure the injection level dependent minority carrier lifetime in silicon wafers. Values as high as 130ms are observed in well passivated high quality and high resistivity float zone wafers.
T. Trupke and R. Bardos, “Photoluminescence: A surprisingly sensitive lifetime technique”, Proceedings 31st IEEE Photovoltaic Specialists Conference. 2005. Orlando, USA.
Demonstration of quasi steady state photoluminescence (QSS-PL) measurements as an extremely sensitive experimental technique to measure the injection level dependent minority carrier lifetime in silicon wafers. Experimental data for the minority carrier lifetime at injection levels <109 cm-3 are presented. The robustness against artefacts resulting from excess carriers in space charge regions (i.e. the so-called DRM effect) is demonstrated.
R.A. Bardos, T. Trupke, M.C. Schubert, and T. Roth, Trapping artefacts in quasi-steady-state photoluminescence and photoconductance lifetime measurements on silicon wafers”, Applied Physics Letters 88 (2006) 053504.
Theoretical analysis and experimental demonstration of the robustness of QSS-PL measurements against artefacts in injection level minority carrier lifetime measurements that result form minority carrier trapping. It is shown that the artificially high lifetimes that are observed in most other lifetime techniques are not observed in QSS-PL.
T. Trupke, R.A. Bardos, M.D. Abbott, and J.E. Cotter, “Suns-photoluminescence: Contactless determination of current-voltage characteristics of silicon wafers”, Applied Physics Letters 87 (2005) 093503.
Experimental demonstration of QSS-PL as a contactless method to measure implied voltages in silicon wafers over a wide range of voltages. Luminescence and Suns-Voc measurements on a bifacial high quality silicon solar cell are presented. It is shown that the luminescence signal can be interpreted as an “implied voltage”. Excellent agreement between Suns-Voc and the voltage obtained from luminescence is observed. This method is useful for the characterisation of high minority carrier lifetime samples at an early stage of production and can be applied even prior to the emitter formation. It can provide quantitative information about the influence of individual processing step on the IV curve.
Luminescence Imaging
T.Fuyuki, H. Kondo, T. Yamazaki, Y. Takahashi, and Y. Uraoka, “Photographic surveying of minority carrier diffusion length in polycrystalline silicon solar cells by electroluminescence”, Applied Physics Letters 86(26) (2005) 262108.
Experimental demonstration of Electroluminescence imaging on small multicrystalline silicon solar cells using a Si CCD camera. A quantitative correlation between the local luminescence intensity and the local diffusion length is reported. The technique is proposed as a fast method for measuring the spatially resolved diffusion length in silicon solar cells.
T. Trupke, R.A. Bardos, M.C. Schubert, and W. Warta, “Photoluminescence imaging of silicon wafers”, Applied Physics Letters 89 (2006) 044107.
First experimental demonstration of PL imaging measurements on large area silicon wafers as a fast experimental technique to measure the spatially resolved minority carrier lifetime. High resolution images are measured with only one second data acquisition time. Excellent quantitative agreement is observed with a Carrier density imaging experiment.
T. Trupke, R.A. Bardos, M.D. Abbott, F.W. Chen, J.E. Cotter, and A. Lorenz, “Fast photoluminescence imaging of silicon wafers”, WCPEC-4, Waikoloa, USA (2006).
Demonstration of PL imaging as an effective quality control tool in photovoltaic research and manufacturing. Qualitative results on fast measurements of the series resistance are presented for the first time. The ability to quickly and reliably identify broken metal grid fingers in PL images measured with current extraction and in EL images is demonstrated.
T. Trupke, E. Pink, R.A. Bardos, and M.D. Abbott, “Spatially resolved series resistance of silicon solar cells obtained from luminescence imaging”, Appl. Phys. Lett. 90 (2007) 093506.
Demonstration of luminescence imaging as a fast experimental method to measure the spatially resolved series resistance quantitatively. The method is based on measuring one luminescence image under open circuit conditions and second illuminated luminescence image with simultaneous current extraction. The requirement to subtract an image measured under short circuit conditions or under reverse bias in order to correct for the diffusion limited effective lifetime is discussed.
P. Würfel, T. Trupke, T. Puzzer, E. Schäffer, W. Warta, and S. Glunz, “Diffusion lengths of silicon solar cells from luminescence images”, Journal of Applied Physics 101 (2007) 123110.
Theoretical analysis and experimental demonstration of a new method to measure the spatially resolved diffusion length in silicon solar cells that is based on measuring the ratio between two luminescence images, each measured with a separate dielectric short pass filters. The method is superior to the method proposed by Fuyuki, as the influence of the laterally variable series resistance is removed. In addition it provides the absolute diffusion length from two non-calibrated images and thus avoids the need for separate calibration.
T. Trupke, R.A. Bardos, M.D. Abbott, K. Fisher, J. Bauer, and O. Breitenstein, Luminescence imaging for fast shunt localization in silicon solar cells and silicon wafers”, International Workshop on Science and Technology of Crystalline Silicon Solar Cells, Sendai, Japan, 2-3 October(2006).
Experimental demonstration of luminescence imaging for fast shunt localisation in silicon solar cells. Various possible industrial applications to mitigate the influence of shunts on production yield are discussed.
M.D. Abbott, T. Trupke, H.P. Hartmann, R. Gupta, and O. Breitenstein, Laser isolation of shunted regions in industrial solar cells”, Progress in Photovoltaics 15 (2007) 613.
Demonstration of the combination of luminescence imaging with laser shunt isolation methods to remove the influence of local shunts on the terminal characteristics of silicon solar cells. A strong improvement in fill factor and open circuit voltage (and thus cell efficiency)is demonstrated on a strongly shunted cell.
D. MacDonald, J. Tan, R.A. Bardos, T. Trupke, “Impurities in solar-grade silicon and their characterisation”, Invited plenary presentation at the 22nd EPVSC, Milan, Italy, 2007.
The detection of the spatially resolved iron concentration in Boron doped silicon wafers from the comparison of photoluminescence images taken before and after breakging FeB pairs is demonstrated.
E. Pink. T. Trupke, R.A. Bardos, M.D. Abbott, Y. Augarten, S. Kontermann, “Fast series resistance imaging using photoluminescence”, 22nd EPVSC, Milan, Italy, 2007, best poster award.
The fast and quantitative detection of the spatially resolved series resistance from luminescence images on various types of silicon solar cells is demonstrated. It is shown experimentally that PL imaging detects series resistance variations from both the front and the rear surface. It is also shown that the quantitative analysis based on four images removes the influence of lateral variations of the diode properties in multicrystalline silicon solar cells.
D. Macdonald, J. Tan, T.Trupke, “Imaging interstitial iron concentrations in boron-doped crystalline silicon using photoluminescence”, J.Appl.Phys., 103, 073710.
The possibility to quantitatively measure the interstitial iron concentration in boron-doped silicon wafers from two luminescence images is demonstrated.
K. Ramspeck, K. Bothe, D. Hinken, B, Fischer, J. Schmidt, R. Brendel, “Recombination current and series resistance imaging of solar cells by combined luminescence and lock-in thermograpy”, Appl.Phys.Lett., 90, 153502, 2007.
A series resistance imaging technique is proposed that is based on a combination of luminescence imaging and lock-in thermography measurements performed on the same cell. The luminescence intensity image is used to get information about the diode voltage and the lock-in thermography measurement for information on the local current density.
D. Hinken, K. Ramspeck, K. Bothe, B, Fischer, R. Brendel, “Series resistance imaging of solar cells by voltage dependent electroluminescence”, Appl.Phys.Lett., 90, 153502, 2007.
A series resistance imaging technique is proposed that is based only on a series of electroluminescence measurements on a silicon solar cell. The method is demonstrated on a monocrystalline silicon solar cell.
M. Kasemann, M.C. Schubert, M. The, M. Koeber, M. Hermle, W. Warta, „Comparison of luminescence imaging and illuminated lock-in thermography on silicon solar cells”, Appl.Phys.Lett., 89, 224102, 2006.
A comparison of luminescence imaging and lock-in thermography on solar cells with different defects. Demonstration of shunt detection in luminescence images and comparison with 2D numerical modelling results.
H. Sugimoto, M. Tajima, “Photoluminescence imaging of multicrystalline wafers during HF etching”, Jap.J.Appl.Phys. 46, (2007) L339-L341.
Demonstration of PL imaging on mc-Si wafers immersed in HF. The resulting surface passivation results in a dramatic increase of the effective minority carrier lifetime and an associated shortening of the required measurement times.
T. Trupke, R.A. Bardos, J. Nyhus, "Photoluminescence charaterization of silicon wafers and silicon solar cells", 18th workshop on Crystalline Silicon Solar cells & Modules 2008, Vail, USA.
The correlation between the minority carrier lifetime and the PL intensity is investigated for a range of multicrystalline wafers from different positions of a cast multi crystalline silicon brick. Absolute lifetime images obtained from luminescence imaging are presented and compared to mircrowave PCD maps. Some fundamental aspects of transient versus quasi steady state minority carrier lifetime measurements are reviewed and some controversial results from the literature are discussed.