Design and fabrication of InAs/GaAs QD based intermediate band solar cells by quantum engineering

The efficiency of a solar cell can be substantially increased by opening new energy gaps within the semiconductor band gap. This creates additional optical absorption pathways which can be fully exploited under concentrated sunlight. Here we report a new approach to opening a sizeable energy gap in a single junction GaAs solar cell using an array of small InAs QDs that leads directly to high device open circuit voltage. High resolution imaging of individual QDs provides experimentally obtained dimensions to a quantum mechanical model which can be used to design an optimised QD array. This is then implemented by precisely engineering the shape and size of the QDs resulting in a total area (active area) efficiency of 18.3% (19.7%) at 5 suns concentration. The work demonstrates that only the inclusion of an appropriately designed QD array in a solar cell has the potential to result in ultra-high efficiency under concentration.