Nondestructive Evaluation of Multijunction Solar Cells for Matching Currents

Nondestructive methods determining current mismatched ratios (CMMRs) between key subcells in a multijunction solar cell were proposed in view of a compensated concept of subcell’s current. Various compensated lights were employed to determine key CMMR of InGaP-InGaAs-Ge related triple-junction (3J) solar cells. When a 405 nm compensated light is used, short-circuit currents of 9.37 mA/cm
²
and 10.28 mA/cm
²
were determined for the InGaP-subcell and InGaAs-subcell, respectively, resulting in a CMMR of 4.4%. Excellent agreement in evaluated properties was obtained when a 532 nm, a 638 nm, and 808 nm compensated lights were used. A 3J solar cell fabricated with an anti-reflected coating was also evaluated. Measured results reveal that an overall short-circuit current of 13.5 mA/cm
²
is still limited by the InGaP-subcell, resulting in a conversion efficiency of 27%. Together with determined short-circuit current of 15.5 mA/cm
²
for the InGaAs-subcell, a possible optimum conversion efficiency of 29.11% is expected.