Rare earths and metal nanoparticles in silicate glass-ceramics to improve the efficiency of photovoltaic solar cells

The efficiency of solar cells may be improved by better exploitation of the solar radiation managing the photons coming from the solar spectrum to better fit the absorption band of the employed solar cells. This can be done by inserting in the front or rear of the solar cell an optically active layer doped with rare earth ions which acts as down-converter or up-converter. This is just one of the possibilities that involve several structures and geometries such as waveguide configuration and radiation trapping systems. Moreover, the use of antenna systems or other sensitizers can improve significantly the optical performance of the down converting layer. In this work we will give a short review regarding the research already developed by the team in the field of down-conversion process and rare earth sensitizing. On the one hand we will focus the attention on the cooperative energy transfer between donor and acceptor ions taking as example the interaction among one Tb³⁺ ion and two Yb³⁺ ions in a 70SiO₂-30HfO₂ glass-ceramic waveguide and the Pr³⁺ to Yb³⁺ energy transfer in bulk fluoride glasses. On the other hand we will show how silver nanoparticles can enhance the absorption efficiency of rare earths.