Voltage and light bias dependent quantum efficiency measurements of GaInP/GaInAs/Ge triple junction devices

III–V monolithic multi-junction solar cells reach efficiencies exceeding 40% and have applications in space and terrestrial concentrator systems. Due to the series connection of the junctions, the external quantum efficiency (EQE) measurement of multi-junction cells presents additional challenges compared to EQE measurement procedures for single-junction devices. Previous work has shown that optimization of bias light and voltage is necessary to minimize measurement artifacts that usually appear during the measurement of the Germanium (Ge) junctions with low shunt resistance. This paper aims to contribute to the improvement of multi-junction device characterization by reporting the effects of low and high shunt resistance junctions on EQE for various voltage and light bias conditions. Voltage and light bias are shown to have different effects on junctions with different shunt resistance. Therefore further investigation of junctions with different shunt resistance under variable light and voltage conditions is needed to provide better understanding of the precise test conditions for EQE measurements. Our results showed that in the high shunt resistance junctions the bias voltage technique is not necessary. However, in the case of junctions with low shunt resistance, a combination of voltage and light bias is required during EQE measurements. Furthermore, the luminescence coupling effect was observed during EQE measurements at very intense light bias conditions confirming previous indications. Finally, an alternative approach for measuring the EQE is proposed.