Plasmon-enhanced downshifting and downconversion: Fundamentals and applications in photovoltaics

Downshifting (DS) and downconversion (DC) are processes in which a high-energy photon is converted into one or several lower-energy photons, respectively. These processes have potential applications in imaging, solar energy harvesting, color conversion, and other fields. The quantum efficiency of DS and DC can be high, even surpassing 100%. However, efficient photon management is crucial for most applications, and improving the yield of DS and DC is highly desirable. One promising and relatively easy way to boost the yield of DS and DC is to utilize plasmonic nanoparticles. The resonant electric field enhancement near plasmonic nanoparticles leads to an increased excitation rate of DS and DC. However, the presence of metallic nanoparticles quenches the emission at both micro and macro scales due to Ohmic losses. Properly balancing enhancement and quenching by choosing the optimal shape, material, size, and concentration of plasmonic nanoparticles has been shown to boost DS and DC by a factor as large as $50\times$. In this review, we discuss the basics of plasmon-enhanced DS and DC and highlight recent progress in this field, covering experimental demonstrations of this concept and its implications for photovoltaics.