Spectral selective and photothermal nano structured thin films for energy efficient windows

This review deals with critical issues in the development of energy-efficient windows from two fundamentally different approaches, namely, spectral selectivity and photothermal effect. This review is therefore divided into two parts. The first part reviews the engineering considerations based on an ideal window concept in terms of spectral selectivity, glazing scale, seasonal factors, and related thermal transfer. In particular, spectrally selective window designs and metal-based thin films are introduced with optimized engineering parameters and physical properties. The second part introduces a new approach of thermal insulation via the photothermal effect of the nanostructured thin films and coatings. The key that limits the heat flow through windows is the thermal insulation, which is traditionally constructed by multi-pane structures with an insulating layer. A novel concept not relying on any insulating media, but photothermal effects of nanomaterial coatings has been recently proposed and experimental verified. Both concepts of spectral selectivity and photothermal effects are introduced for energy-efficient window applications. A new direction is proposed in the development of the energy-efficient windows via the photothermal effects in various nanostructures of thin films and coatings.