One way to increase the efficiency of a photovoltaic (PV) system is to selectively control which light wavelengths can reach the semiconductor. This is particularly useful for concentrated light designs (i.e. using mirrors and optics to direct more light to the PV cell), where longer wavelengths can generate enough heat to raise the panel temperature, reducing efficiency.

One method of controlling the incident wavelengths is to use tandem cells. These are cells with multiple semiconductor layers, each layer with a different bandgap capable of operating on a different region of the electromagnetic spectrum. Another method is to use optical filters to either reflect unwanted wavelengths or redirect them towards a solar-thermal device. More can be read about beam splitting here.

The University of New South Wales in Australia combined four different cells to create a photovoltaic system which achieved a system efficiency of 40.4% in concentrated sunlight. This level of efficiency is the highest value that’s been reported to date for sunlight conversion. The research for this project was conducted in a partnership with Raygen Resources, who’s website can be found here.