Analysis of subcell open-circuit voltages of InGaP/GaAs dual-junction solar cells fabricated using hydride vapor phase epitaxy

Abstract

The current–voltage (I–V) characteristics of the individual subcells of InGaP/GaAs dual-junction (DJ) solar cells fabricated using hydride vapor phase epitaxy were investigated by electroluminescence (EL) and external quantum efficiency measurements. In particular, we found the radiative recombination efficiency of the InGaP single-junction (SJ) cell was lower by a factor of 40 than that of GaAs SJ cells because the InGaP SJ cell did not have any passivation layer at the front surface. By taking each radiative recombination efficiency into account, we accurately projected I–V curves of each subcell in the InGaP/GaAs DJ cell. By combining the projected I–V curves with short-circuit current density obtained experimentally from light I–V measurements, the open-circuit voltage (Voc) was determined to be 1339 mV for the InGaP top cell and 978 mV for the GaAs bottom cell, respectively, which were consistent with the experimentally obtained Voc values of each SJ cell.