Bismuth-doped oxide glasses as potential solar spectral converters and concentrators

The efficiency of photovoltaic energy conversion processes is often limited by the fact that electronic properties, band-gap and reflectivity of the employed cell ( or cell material) and the spectral distribution of sunlight do not sufficiently match. In this context, solar spectral converters and concentrators that rely on the use of luminescent materials to either convert or redirect incoming sunlight are presently receiving renewed interest. In this study, various bismuth-doped oxide glasses were considered for these applications. It is shown that such glasses exhibit broad luminescence in the near infrared spectral range ( NIR) upon excitation with soft ultraviolet to visible light ( UV-VIS), originating from Bi-based emission centers. Strong absorption in the blue-green but high transmission at wavelengths larger than similar to 800 nm as prerequisite for efficient luminescence concentrators, and optical homogeneity and solar-thermal stability provide important advantages over potential alternatives. It is demonstrated that the considered glasses are particularly interesting in combination with low-bandgap semiconductors, e.g. GaSb, Ge or InAs. Using Bi-doped glasses as UV-VIS -> NIR down-converters would not only lead to significant extension of the operation window of such cells, but also strongly improve their overall efficiency under solar or thermal irradiation.