Photoluminescence-Based Current–Voltage Characterization of Individual Subcells in Multijunction Devices

We demonstrate a photoluminescence (PL)-based contactless method to determine the current-voltage (I-V ) characteristics of the individual subcells in a multijunction solar cell. The method relies upon the reciprocity relation between the absorption and emission properties on a solar cell. Laser light with a suitable energy is used to excite carriers selectively in one junction (1J), and the internal voltages are deduced from the intensity of the resulting luminescence. The I-V curves obtained this way on 1J, 2J, and 6J devices are compared with those obtained using electroluminescence (EL). Good agreement is obtained at high-injection conditions, while discrepancies at low injection are attributed to in-plane carrier transport.