Toward high-efficiency solar upconversion with plasmonic nanostructures

Upconversion of sub-bandgap photons can increase the maximum efficiency of a single-junction solar cell from 30% to over 44%. However, upconverting materials often have small absorption cross-sections and poor radiative recombination efficiencies that limit their utility in solar applications. Here, we show that the efficiency of upconversion can be substantially enhanced with a suitably designed plasmonic nanostructure. The structure consists of a spherical nanocrescent composed of an upconverter-doped dielectric core and a crescent-shaped metallic shell. Using numerical techniques, we calculate a greater than 10-fold absorption enhancement for a broad range of sub-bandgap wavelengths throughout the entire upconverting core. Further, this nanocrescent enables a 100-fold increase in above-bandgap power emission toward the solar cell. Our results provide a framework for achieving low-power solar upconversion, potentially enabling a single-junction solar cell with an efficiency exceeding the Shockley–Queisser limit.