Optical considerations for automotive windshields with improved thermal performance

Among the many requirements to modern high-performance automotive windshields is to provide a good visibility while limiting the amount of sunlight heat energy entering the cabin. This is traditionally achieved by incorporating a sputter deposited silver-inclusive solar-control coating into the windshield laminate to boost its reflection in the near-infrared. Such a coating can also serve as a heating element for the windshield deicing. This article discusses the benefit of using an additional coating deposited on the innermost surface of the windshield to further improve its thermal insulation properties, particularly in the mid-infrared spectral region. A systematic approach is employed to prioritize the contribution of sputter deposition parameters and thin-film design elements to the enhanced combined optical and electrical attributes of both coatings. Refined simulation models are presented and put to the test to attain the required level of visible transmittance. The additional benefit of adding the thermal coating for an improved color neutrality is also discussed.