  Indoor heating during winters accounts for a significant portion of energy
consumed by buildings in regions of cold climate. Development of transparent
coatings for windows that efficiently harvest solar energy can play a major
role in reducing energy consumption and fuel costs incurred for winter heating.
In recent years, there has been a great research effort towards designing
transparent solar absorber coatings using nanophotonic structures. The
potential of coatings based on planar multilayer structures, however, has
received very little attention. In this work we investigate the performance of
planar multilayer thin films using low cost materials for design of transparent
solar absorber window coatings. Our study led to the proposal of two planar
multilayer designs. Simulation results predict that an increase in surface
temperature by 21 K and 25 K, while maintaining mean visible transmittance of
over 60% is possible using these designs. These results illustrate the great
promise planar multilayer structures hold for winter thermal management of
buildings.
