Luminescent borate glass for efficiency enhancement of CdTe solar cells

Rare-earth (RE) doped borate glasses are investigated for their potential as photon down-shifting cover glass for CdTe solar cells. The barium borate base glass is doped with trivalent rare-earth ions such as Sm3+, Eu3+, and Tb3+ showing an intense luminescence in the red (Sm3+, Eu3+) and green (Tb3+) spectral range upon excitation in the ultraviolet and blue. Additionally, the glasses are double-doped with two RE ions for a broad-band absorption. The gain in short-circuit current density of CdTe solar cells with different thicknesses of the CdS buffer layer is calculated. Though the single-doped glasses already reveal a slight increase in short-circuit current density, the double-doped glasses allow for higher efficiency gains since a significant broader spectral range is covered for absorption. For a Tb3+/Eu3+ double-doped glass with a RE doping level of 1 at% each, an efficiency increase of 1.32% can be achieved.