NOTICEThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party's use or the results of such use of any information, apparatus, product, or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights. The physical properties of thin films affect the performance and durability of nearly every solar energy conversion device. Familiar examples of thin films for solar applications are optical materials and protective coatings. Optimized optical properties are key to cost-effective photothermal conversion where individual components must have high absorptance, reflectance, or transmittance. The protection of sensitive substrates from corrosion and/or erosion is essential to ensure adequate component and system lifetime. Such substrates range from photovoltaic materials operating near room temperature to turbine blade structural alloys in hostile environments at very high temperatures (>1 000° C). Although much has been written on particular categories of thin-film materials for solar energy (for example, absorbers for receiver surfaces), to date no one has provided an overview of the spectrum of applications for passive thin films in solar energy. This work is such an overview and also reviews the material state of the art as described in the current literature. Active thin film devices such as photovoltaics and thermoeleetrics are not discussed.This report has been completed as part of the FY79 Materials Branch Research Task 3122.30. It also serves as a chapter in the forthcoming book Properties of Polycrystalline and Amorphous Thin Films and Devices, published by Academic Press and edited by L. L. Kazmerski. This limited access report is being distributed with the permission of the publisher and should not be reproduced further. A remarkable number of applications exist for thin-film technology across the spectrum of solar energy conversion devices. Passive films, defined to exclude those applications such as thermoelectrics and photovoltaics where the film itself is the primary transducer or conversion element, are critical to nearly every solar technology. The category of passive thin films as defined in this chapter includes optical films, protective coatings, high and low energy surfaces, and selective membranes • Optical films for solar energy conversion systems include absorber, reflector, and enhanced transmitting (antireflection) materials; heat mirrors, and transparent conducting electrodes. Specialty films are also required for particular applications such as switchable optical materials, films that have a high transmittance in the photosynthetic spectral region with a high reflectance or absorptance elsewhere, and ultraviolet (UV) reflecting or absorbing interference films. As important elements of the space pro...
