This work involves the study of the positive emittance-switching (i.e. emittance that increases with increasing the temperature) of thermochromic VO2 films deposited using reactive pulsed laser deposition (RPLD) on Al substrates. The temperature dependence of the emittance of a 260 nm-thick VO2 film on Al substrate revealed a maximum of the emittance of 0.29 around 68 degrees C. It is attributed to an increase in the infrared radiation absorption by the VO2 film due to the coexistence of both insulating and metallic phases in the vicinity of the transition temperature of VO2. The emittance tunability between 25 degrees C and 68 degrees C is 0.21. Since practical SRD application requires both high emittance at high temperature and large tunability, we demonstrate, by both simulation and fabrication, that these goals can be accomplished to some extent by a top dielectric a-Si:H/SiO2 lambda/4 stack layer. In fact, the addition of a-Si:H/SiO2 lambda/4 over-layer results in an increase of the maximum value of the emittance by 114% (from 0.29 to 0.62) as well as an increase of the tunability by 81% (from 0.21 to 0.38). This work reports an important improvement of the positive emittance-switching efficiency of the VO2-based structures and holds promise for a new generation of smart radiator devices (SRDs) for a passive thermal control of spacecrafts. (C) 2013 Elsevier B. V. All rights reserved.