Determination of subcell I-V parameters by a pulsed suns-Voc method including optical coupling
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The open circuit voltage of a single subcell in a multijunction cell stack can be measured with the help of pulsed, millisecond illumination. This concept makes use of the fact that the charging of the non-illuminated cell capacitances takes place on a much longer timescale than of the illuminated one. Optical coupling introduces a photocurrent in the subcell underneath. Its efficiency can be quantified in parallel under short circuit conditions. A suns-Voc approach, applied to this subcell pair, yields all relevant diode parameters. Applied to all subcells of a GaInP/GaInAs/Ge triple junction cell, a very good match to the dark I-V curve is obtained.