Holographic spectrum splitter for ultra-high efficiency photovoltaics
To move beyond the efficiency limits of single-junction solar cells, junctions of different bandgaps must be used to avoid losses from lack of absorption of low energy photons and energy lost as excited carriers thermalize to the semiconductor band edge. Traditional tandem multijunction solar cells are limited, however, by lattice-matching and current-matching constraints. As an alternative we propose a lateral multijunction design in which a compound holographic optic splits the solar spectrum into four frequency bands each incident on a dual-junction, III-V tandem cell with bandgaps matched to the spectral band. The compound splitting element is composed of four stacks of three volume phase holographic diffraction gratings. Each stack of three diffracts three bands and allows a fourth to pass straight through to a cell placed beneath the stack, with each of the three gratings in the stack responsible for diffracting one frequency band. Generalized coupled wave analysis is used to model the holographic splitting. Concentration is achieved using compound parabolic trough concentrators. An iterative design process includes updating the ideal bandgaps of the four dual-junction cells to account for photon misallocation after design of the optic. Simulation predicts a two-terminal efficiency of 36.14% with 380x concentration including realistic losses.
Additional Information© 2013 Society of Photo-Optical Instrumentation Engineers (SPIE). The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000333. The authors acknowledge the Dow Chemical Company for funding. Thanks to E. Kosten for useful discussion.
Published - 882105.pdf