Fig. 1: Motivation of the investigated photonic upconverter device.
From: Experimental validation of a modeling framework for upconversion enhancement in 1D-photonic crystals
a Approach of utilizing sub-bandgap photons for charge generation in a solar cell by a photonic upconverter on the rear side. b Scanning electron microscope (SEM) image of the realized 1D-photonic structure made of TiO2 and PMMA with embedded upconverter nanoparticles (UCNPs). c SEM image of upconverter nanoparticles. d Schematics of core-shell upconverter nanoparticles of NaYF4:Er3+, converting near infrared (NIR) to NIR and up to visible (VIS) photons in the active core. The inert shell prevents losses due to surface quenching. e Energy levels in the upconverter Er3+ and the upconversion (UC) process influenced by photonic effects of the surrounding structure: increased absorption due to a locally enhanced energy density, non-linearly increasing the probability of an energy transfer UC process, followed by UC emission from a higher level that can be enhanced due to a modified local density of optical states.
