Rare-Earth Ion-Based Photon Up-Conversion for Transmission-Loss Reduction in Solar Cells

Photon up-conversion (UC) describes an anti-Stokes emission process, in which a luminophor emits one higher energy photon after being excited by multiple low-energy photons, among which rare-earth (RE) ion-doped materials present promising UC properties due to unique electron configuration. RE UC materials have been widely studied in solar cells with the purpose to reduce transmission losses, i.e., achieve wide/full solar spectral harvesting and high-power conversion efficiency, by converting unutilized sub-bandgap photons into sensitive resonant photons. This chapter exclusively focuses on RE-doped UC materials and their applications in solar cells. The RE-based UC photophysics, UC enhancement, and applications in solar cells will be reviewed and briefly discussed.