Optical and structural properties of d0 ion-doped silicate glasses for photovoltaic applications

Optical and structural properties of float-type soda-lime-silica (SLS) glasses doped with 0.2 mol % TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, MoO3 or WO3 have been studied. Under ultraviolet excitation all d doped glasses exhibit broadband visible emission centred between 19 000 and 25 000 cm(-1) (400-525 nm) due to a transition from the 2p orbital of O2- to the metal d orbital. Dopant additions lead to shifts in the ultraviolet absorption edge to lower energies, with doped glasses having an absorption edge 2000 cm(-1) (similar to 20 nm), and in the case of MoO3, 4000 cm' (similar to 40 nm), shifted relative to the corresponding undo ped glass. Combined ultraiolet-visible absorption and X-band EPR spectroscopy analyses confirm that dopant cations occur in the studied glasses in the expected oxidation states of Ti4+, Zr4+, Hf4+, Nb5+, Ta5+ Mo6+ and W6+, although very low levels of Mo5+ are also observed, as demonstrated by the EPR resonance at g=1.92 (3.7 T). The incorporation of the studied dopants into SLS glasses may find applications as cover glasses in photovoltaic (PV) applications, providing ultraviolet protection of polymers and solar cell materials in PV units whilst enhancing solar cell efficiency through downconversion/fluorescence of absorbed ultraviolet photons with re-emission as visible photons, available for absorption and conversion by the solar cell material.