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7 March 2014 Cutoff wavelength optimization for high-efficiency split spectrum photovoltaics
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Split spectrum photovoltaics, where incident light is divided onto multiple cells on the basis of wavelength, are an exciting recent development in the solar energy field. This technology has the potential to exceed record conversion efficiencies by utilizing a large number of p-n junctions while mitigating the constraints that plague monolithic cells: lattice matching and current matching. Each cell in a split spectrum system can have a different lattice constant (allowing for more combinations of materials) and to have different operating currents (allowing for more combinations of band spacing). In this work, we examine a split spectrum system utilizing a single spectrum splitting device (a dichroic filter) to divide the solar spectrum onto two cells. Whereas many split spectrum designs use numerous filters to direct light onto single junction cells, in this system each cell is composed of multiple active junctions. Each cell is then tailored to absorb a portion of the solar spectrum. The combination of the two cells allows for four, five, or more active junctions while maintaining lattice and current matching conditions in each cell. A number of different cutoff frequencies for the dichroic filter are examined. Each cutoff frequency corresponds to its own combination of ideal band placements for both the shorter and longer wavelength cells. Materials corresponding to those band placements are examined to determine if any combinations can satisfy lattice matching parameters; designs which do are then simulated using TCAD Sentaurus.
Chandler Downs and Thomas E. Vandervelde "Cutoff wavelength optimization for high-efficiency split spectrum photovoltaics", Proc. SPIE 8981, Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III, 89810D (7 March 2014);


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