ILLUMINATED LOCK-IN THERMOGRAPHY (ILT) –NEW METHOD FOR SPATIALLY RESOLVED ASSESSMENT OF POWER LOSSES IN SOLAR CELLS

摘要

Lock-In Thermography as established for the detection of shunts in solar cells a few years ago by O.Breitenstein and M. Langenkamp (Proc. 2nd WCPEC, Wien, Austria, 1998) has meanwhile become a powerful tool for the detection of technological failures in solar cell processing. A drawback of the method is, that the solar cell investigated is operated in an un-illuminated state. Thus dark current paths are measured and the dissipation ofpower follows the dark characteristics. This article presents a method that allows Thermography measurementsunder illuminated conditions in solar cells as well as emitter diffused wafers using a semiconductor laser aschopped excitation source. It will be shown that this new method – Illuminated Lock-In Thermography – allows thespatially resolved assessment of power losses in solar cells under conditions, which are considerably closer to thereal operation conditions of a solar cell than the methods available previously. Illuminated Lock-In Thermographyenables the investigation of power losses due to single grain boundaries in silicon. Power losses due to differentrecombination channels as well as losses in series resistance may be measured quantitatively. As the method gives adirect measure of all power losses in a solar cell under operation conditions, an assessment of the impact ofdifferent loss mechanisms on the solar cell performance is easily attainable.