A structure is disclosed which comprises a thermochromic layer located between a front layer and a back layer, wherein the front layer is a dielectric and is in contact with the thermochromic layer, and wherein the back layer is reflective to infrared (IR) radiation. Below the thermochromic transition temperature of the thermochromic layer, the front layer and thermochromic layer are IR-transparent, so the structure is highly reflective to IR radiation because of the presence of the reflective back layer. Consequently, the structure has a low emittance in this state. Above the thermochromic transition temperature of the thermochromic layer, the device structure becomes IR-absorbent, so the reflectance of the structure is reduced and hence its emittance is increased. The front layer index-matches with the thermochromic layer above the transition temperature of the thermochromic layer to enable radiation to enter the thermochromic layer.