Preparation and characterisation of solar selective SnOx:F coated aluminium reflector surfaces

Abstract The preparation and characterisation of spectrally selective reflector surfaces of pyrolytically deposited fluorine-doped tin oxide (SnOx:F) on aluminium is reported. The pyrolytically deposited doped tin oxide layer offers spectral selectivity to the aluminium surface. The SnOx:F films were grown at temperatures between 380 and 450°C, with film thickness varying in the range 200–800 nm. X-Ray diffraction, atomic force microscopy, and scanning electron microscopy have been performed on the tin oxide surfaces, and an approximate grain size of 50–300 nm is indicated. Hall effect and resistivity measurements were carried out for SnOx:F films deposited on glass under the same conditions as for those on aluminium. Resistivities in the range 6–19×10−6 Ωm, with carrier concentrations of between 1.1 and 5.3×1020 cm−3, and hall mobilities of 16.8–30.7 cm2 V−1 s−1 were obtained using the van der Pauw method. Solar reflectance calculations were made using the standard AM1.5 solar irradiance spectrum. High solar reflectance was obtained for wavelengths below 1.1 μm, and low solar reflectance for wavelengths above 1.1 μm; the best sample had Rcell and Rtherm values of 0.749 and 0.558, respectively, for the SnOx:F/Al film structure. Spectral selectivity was highly dependent on the preparation conditions, doping, and thickness of the films.