Improving the visible transmittance of low-e titanium nitride based coatings for solar thermal applications

Low-emissivity (low-e) coatings on glass are nowadays extensively used for energy saving applications in architectural windows and on solar thermal collectors. In this work the feasibility of TiN-based layers as low-e coatings has been studied. TiN samples were deposited by reactive magnetron sputtering and, in order to improve their optical properties (transmission in the visible range, T and emissivity, ɛ), we have investigated the changes in optical response following three different approaches: (i) post-deposition annealing treatments up to 500 °C, (ii) doping the TiN layers with aluminium (target composition: Ti/Al = 90/10, 75/25 and 50/50) and (iii) deposition of antireflective coatings of TiO2 in multilayers structures. The crystalline structure and chemical composition of the multilayers were studied by X-Ray Diffraction and Rutherford Backscattering Spectroscopy, respectively. Spectroscopic Ellipsometry, Fourier Transform Infrared Spectroscopy and direct emissivity measurements were employed to determine the optical properties T and ɛ. We have concluded that the most noticeable improvement has been obtained by the deposition of multilayers structures increasing in a 30% the original transmittance of the single TiN coatings.