Thin Solid Films, Vol.398-399, 65-70, 2001
The influence of film composition on the optical and thermal properties of solar control coatings
ATOFINA has developed a new type of solar control glazing product, Certincoat((R)) SunE((TM)), that combines the properties of high solar absorption in the near infrared region of the spectrum and low emissivity with neutral reflected color, high visible light transmission, and low haze in a simple two-layer coating based on doped tin oxide. When the dopant is antimony, the tin oxide layer (TOSb) absorbs solar energy; when the dopant is fluorine, the tin oxide (TOF) reflects mid-range infrared radiation. SunE((TM)) coatings can be deposited under typical atmospheric-pressure chemical vapor deposition (APCVD) conditions used by existing manufacturers of low emissivity products, utilizing readily available organotin precursors, such as monobutyltin trichloride or dimethyltin dichloride. Using optical models and laboratory experimentation, we have found that glazings with a neutral reflected color can be produced over a wide range of visible transmission (43-71%) and solar heat gain coefficient (0.47-0.60, center of glass) without the incorporation of a traditional iridescence-suppressing layer. The neutral reflected color depends predominately on the thickness of the individual layers and less so on the antimony content of the TOSb layer. Films with neutral reflected color are obtained for all antimony concentrations from approximately 3 to 15% when TOSb/TOF layers of approximately 240/300 nm are combined. The transmission and solar heat gain are primarily inverse functions of the antimony content. Film haze greater than 1% is generally due to surface roughness and can be reduced by as much as 40% by the inclusion or exclusion of certain additives, such as trifluoroacetic acid and/or water, during the early stages of the deposition process. Windows in both single and double pane configurations can be fashioned with SunE((TM)) that meet or exceed the Energy Star window-labeling specifications of the US Department of Energy for Southern climate zones.