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Characterizing GaInP/GaInAs/Ge Multijunction Solar Cells With Electroluminescence
T. Kirchartz, A. Helbig, M. Hermle, U. Rau, A.W. Bett
Multijunction Solar Cell, Electroluminescence, Current Voltage Curves
Advanced Photovoltaics
Subtopic: Fundamental Studies
Event: 23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain
Session: 1AO.6.4
86 - 89
ISBN: 3-936338-24-8
Paper DOI: 10.4229/23rdEUPVSEC2008-1AO.6.4
0,00 EUR
Document(s): paper


We show how characterization of GaInP/GaInAs/Ge multijunction solar cells benefits from the use of electroluminescence (EL) measurements. Usual characterization methods involving optical excitation and measurement of electrical response are challenging when they are applied to multijunction concentrator cells due to the necessity of high optical power and the precise simulation of sunlight. By inversing the direction of excitation and response, individual information about the subcells becomes accessible at high injection conditions. We show how to use an electro-optical reciprocity theorem that describes the link between solar cell quantum efficiency and electroluminescent emission to extract the current/voltage curves of the individual subcells from EL spectra. This is accomplished by comparing the spectra with the solar cell quantum efficiency and an independently measured current/voltage curve. The comparison with the solar cell quantum efficiency allows us to determine the relative voltage differences between the three junctions, while the current/voltage curve allows us to adjust the offset of the voltage axis. The final results are internal voltages at all currents, where the spectra were measured. This information yields for example the individual diode quality factors of the cells as well as the difference to their respective radiative limits.