Investigation of the open-circuit voltage in wide-bandgap InGaP-host InP quantum dot intermediate-band solar cells

To analyze the open-circuit voltage (Voc) in intermediate-band solar cells, we investigated the current-voltage characteristics in wide-bandgap InGaP-based InP quantum dot (QD) solar cells. From the temperature dependence of the current-voltage curves, we show that the V-oc in InP QD solar cells increases with decreasing temperature. We use a simple diode model to extract V-oc at the zero-temperature limit, V-0, and the temperature coefficient C of the solar cells. Our results show that, while the C of InP QD solar cells is slightly larger than that of the reference InGaP solar cells, V-0 significantly decreases and coincides with the bandgap energy of the InP QDs rather than that of the InGaP host. This V-0 indicates that the V-oc reduction in the InP QD solar cells is primarily caused by the breaking of the Fermi energy separation between the QDs and the host semiconductor in intermediate-band solar cells, rather than by enhanced carrier recombination. (c) 2018 The Japan Society of Applied Physics.