Efficiency enhancement in solar cells using photon down-conversion in Tb/Yb-doped tellurite glass

Management of the solar spectrum incident on a solar cell was studied using tellurite glasses doped with Tb3+ and Yb3+ ions as a cover slip. From the transmittance measurements through the doped glass, a red-shift of the solar spectrum was observed and the mechanisms involved in this phenomena were investigated through the absorption spectra and luminescent measurements. Energy transfer of the UV radiation into VIS and IR radiation was elucidated by analyzing the emission spectra. From the results, the power dependence of the Yb3+ IR luminescence on the pumping laser intensity at 482 nm revealed that the energy transfer mechanism involving a virtual state was predominant in these samples. Total quantum efficiency higher than 100% was obtained for the sample co-doped with 1% of Tb3+ ions and 5% of Yb3+ ions. The efficiency of commercial Silicon and Gallium Phosphide (GaP) solar cells, covered with tellurite glasses doped with Tb3+ and Yb3+ ions, was measured and compared to the efficiency with an un-doped the cover glass. Efficiency enhancement was observed with a dependence on the rare earth ions concentrations, and the results were attributed to the modification of the spectral profile of the incident radiation in the IR region.