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

Optical and structural properties of float-type soda lime silicate (SLS) glasses doped with 0.2 mol % TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, MoO3 or WO3 have been studied. Under UV excitation all d0 doped glasses exhibit broadband visible emission centred between 19,000 cm-1 and 25,000 cm-1 (400nm – 525nm) due to a transition from the 2p orbital of O2- to the metal d0 orbital. Dopant additions lead to shifts in the UV absorption edge to lower energies, with doped glasses having an absorption edge 2,000 cm-1 (~20nm), and in the case of MoO3, 4,000 cm-1 (~40nm), lower than the corresponding undoped glass. Combined UV-Vis 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 (3.7T). The incorporation of the studied dopants into SLS glasses may find applications as cover glasses in photovoltaic (PV) applications, providing UV protection of polymers and solar cell materials in PV units whilst enhancing solar cell efficiency through downconversion / fluorescence of absorbed UV photons with re-emission as visible photons, available for absorption and conversion by the solar cell material.