Temperature dependence of photocurrent components on enhanced performance GaAs/AlGaAs multiple quantum well solar cells

The performance of Al0.36Ga0.64As p/i/n solar cells with multiple quantum w ells (MQW) of GaAs/Al0.36Ga0.64As in the i-region has been investigated at various temperatures, ranging from - 10 degreesC to 100 degreesC, and compa red with that of conventional solar cells composed of either the quantum we ll material (GaAs) or the barrier material (Al0.36Ga0.64As) alone. The dark currents of the MQW cells were found to lie between those of the conventio nal cells. The increase of dark current with temperature was accompanied by a slight decrease of the diode ideality factor. A linear dependence of ope n-circuit voltage (V-oc) on temperature was observed for all cells when ill uminated with a 100W halogen lamp. V-oc for the MQW cells was found to be i ndependent of the number of wells, lying between the V-oc's for the two con ventional cells. The MQW cells exhibited performance improvement with tempe rature when compared to the conventional cells and there was a significant enhancement in the short-circuit current with temperature of those MQW cell s that exhibited poorer performance at lower temperatures. Theoretical calc ulations have quantified the contribution of the tunneling current componen t to the total observed photocurrent at the various temperatures examined. It was found that tunneling currents are present at all temperatures and ca n be the dominant component in MQW cells of thinner wells at low temperatur es. These results suggest that GaAs/Al0.36Ga0.64As MQW structures, of good- quality material, when processed as conventional solar cells with antirefle ctive coatings should deliver more output power under intense illumination than conventional solar cells composed of the quantum well material alone. (C) 2001 Elsevier Science B.V. All rights reserved.