Effect of Barrier Thickness on Carrier Transport Inside Multiple Quantum Well Solar Cells Under High-Concentration Illumination

Carrier transport inside InGaAs/GaAs/GaAsP multiple quantum well (MQW) solar cells was discussed under high-concentrated sunlight illumination up to 338 suns. Current-voltage (I-V) characteristic curves for a GaAs reference cell and MQW cells with GaAsP barrier thickness of 2, 4, and 6 nm were investigated under dark and high-concentration illumination. Carrier collection efficiency (CCE) was estimated by net photocurrent, which is the difference between illuminated current and dark current density at each bias voltage normalized by the value at the saturated point. For the 2-nm barrier, CCE exhibited almost no degradation compared with the GaAs reference cell. On the other hand, CCE for the 6-nm barrier degraded with forward biases as the sunlight concentration ratio increased. The degradation in CCE under a high-concentration ratio is shown to be the result of carrier accumulation in quantum wells. Thin barriers seemed to eliminate such accumulation with the help of the carrier tunneling effect through the barriers.