Nature Nanotech. 9, 126–130 (2014)

Thermophotovoltaic cells are a new breed of hot solar cell. They absorb sunlight and convert it into thermal emission, which then drives electricity generation in a photovoltaic cell. As the absorber can be engineered to capture the entire solar spectrum, this approach is attractive for harnessing all the energy present in sunlight. The feasibility of the scheme has already been reported, but the difficulties in engineering such devices have limited their operational efficiencies to ∼1%. Now, Andrej Lenert and co-workers from Massachusetts Institute of Technology in the USA have shown that, by employing multiwalled carbon nanotubes as an absorber and a Si/SiO2 photonic-crystal structure as a thermal emitter, it is possible to reach an operational efficiency of 3.2% under concentrated (×750) solar illumination. The highest efficiency is obtained at a temperature of about 1,235 K. The team believes that even better efficiencies should be achievable by employing InGaAsSb photovoltaic cells that have higher fill factors, open-circuit voltages and active areas.