Advances in up- and down-converted fluorescence for high efficiency solar cells using rare-earth doped fluorozirconate-based glasses and glass ceramics

Transparent, rare-earth doped fluorozirconate-based glasses and glass ceramics are attractive systems as up- and downconverters to increase solar cell efficiency. For down-conversion applications, the efficiency of a silicon solar cell could be significantly increased in the ultraviolet spectral range by placing a europium-doped glass ceramic on top. High transparency is a key issue here to avoid scattering losses and to obtain high light output. Transmission spectra of fluorozirconate glasses, which were additionally doped with chlorine ions to initiate the growth of BaCl2 nanoparticles therein upon thermal annealing, show that the absorbance in the visible spectral depends significantly on the annealing conditions. For up-conversion applications, erbium-doped fluorozironate glasses have been investigated. 2-dimensional intensity mapping of the up-converted fluorescence yielded information on the homogeneity of the glass sample and the erbium distribution therein. Depth scan experiments showed that the position of the focus of the excitation laser beam plays a crucial role since saturation of the 2-photon up-conversion occurs for high excitation power.