Transparent heat mirrors for solar-energy applications.

Transparent heat-mirror films, which transmit solar radiation but reflect ir thermal radiation, have potentially important applications in solar/thermal/electric conversion, solar heating, solar photovoltaic conversion, and window insulation. We have used rf sputtering to prepare two types of films: TiO(2)/Ag/TiO(2) and Sn-doped In(2)O(3). To characterize the properties of heat-mirror films for solar-energy collection, we define the parameters alpha(eff), the effective solar absorptivity, and epsilon(eff), the effective ir emissivity. For our Sn-doped In(2)O(3) films, alpha(eff)/epsilon(eff) is comparable to the values of alpha/epsilon reported for the leading selective absorbers. Even higher values of alpha(eff)/epsilon(eff) are obtained for the TiO(2)/Ag/TiO(2) films.