Potential for low dimensional structures in photovoltaics

Photovoltaics presently represents the fastest growing sector of the electricity generation industry, although growing from a small base. Energy conversion efficiency is a key parameter with this technology since it directly impacts both material and deployment costs. The performance of the traditional bulk semiconductor solar cell is limited to about 33% while thermodynamic limits on the conversion of sunlight to electricity are much higher at 93%. Low dimensional structures appear capable of allowing much of this gap to be bridged. These structures allow increased flexibility with traditional efficiency enhancement approaches such as those based on ‘stacked’ or tandem cells, which double efficiency limits to 66%. Perhaps more interestingly, they offer scope for completely new device concepts such as those relying on excitations between multiple energy bands and improved ‘hot-carrier’ cells, that offer scope for similarly high performance.