Transient analysis of luminescent coupling effects in multi-junction solar cells

We investigate the luminescent coupling (LC) effects in a four-junction GaInP/GaAs//GaInAsP/GaInAs concentrator solar cell based on transient open-circuit voltage (V-oc) measurements under monochromatic illumination. Photocurrent generation in the non-absorbing GaInAs bottom subcell due to LC from upper subcells shows superlinear behavior with increasing light intensity. Along with this, a V-oc enhancement is observed and quantified for illumination intensities that span almost six orders of magnitude. The V-oc increase is explained and studied using a series-connected diode model including subcell shunt resistances, capacitances, and LC effects. The impact of unilluminated subcells on the subcell V-oc determination is discussed for multi-junction solar cells. Finally, in the analysis of the LC generated photocurrent, namely, the coupling factor from the GaInAsP to the non-absorbing GaInAs subcell, a characteristic dependency on bias voltage is shown and explained by a result of competing photo-and electroluminescence mechanisms. Published by AIP Publishing.