Carbon Nanotube - Quantum Dot Nanostructures for Ultra-high Efficiency Photovoltaics

Space applications continue to be limited by the availability of cost-effective power. Significantly higher efficiency cells with lower mass and volume are required to improve performance and lower mission costs; however, improvements in conventional multijunction technology are not expected to meet the necessary performance increases. Instead, new materials and mechanisms are needed to obtain the required efficiency levels. We propose a nanostructured material consisting of semiconductor quantum dots (QDs) and arrays of carbon nanotubes (CNTs) to produce photovoltaic devices with ultra-high efficiencies. QDs and CNTs exhibit critical material properties that are important to achieving ultra-high efficiency photovoltaics. By combining several sizes of QDs and different QD materials, the absorbing layer may be optimally matched to the solar spectrum. In addition, QDs increased oscillator strengths result in more efficient absorption. This allows for a thinner absorber layer and therefore the opportunity to increase the efficiency of charge collection. CNTs are the ideal material for carrier collection as they can exhibit excellent conductivity and their energy levels are well-positioned for charge transfer from the QDs to the CNTs. The proposed ultra-high efficiency devices will create significant opportunities for space-based applications by lowering mission costs while increasing available power.