Structural, optical and mechanical properties of Ti-doped Ta2O5 films for PV glass covers

Ti doped Ta2O5 thin films (TTO) with uniform thickness were prepared on photovoltaic glass substrates by DC and RF magnetron co-sputtering with different target powers. The surface morphology and microstructure of the films were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM). The composition of the films was analyzed by X-ray photoelectron spectroscopy. The optical parameters of the films were measured by UV-visible spectrophotometer. The hardness and Young 's modulus of the coating were tested by nanoindentation. XPS analysis shows that the main components of TTO films are TiO2 and Ta2O5. SEM and AFM results show that the surface of the TTO film is smooth and flat, with uniform elemental distribution and nanometer roughness. The SEM cross-sectional morphology shows that the TTO film presents a dense columnar structure growth. The TEM results show that the TTO films do not show bright diffraction rings and mainly exhibit an amorphous phase structure dominated by Ta2O5. The optical test results show that the maximum transmittance of TTO film can reach 94.59 %. The transmittance of TTO films shows a decreasing trend with increasing sputtering power of the target, while the opposite is true for reflectance and refractive index. The optical band gap of the TTO films is between 4.12 eV and 4.42 eV. The mechanical test results show that the hardness of the TTO film can reach up to 9.53 Gpa. The hardness of TTO film increases with the increase of target power. The H/E and H3/E2 values indicate that Ti doped Ta2O5 films are favourable for improving the resistance to plastic deformation of the films. Comprehensive analyses show that Ti doped Ta2O5 films can have both excellent optical and mechanical properties. TTO films can provide a valuable reference for the study of PV glass protective layer.