Study of annealing effect upon the structural and solar- selective properties of C/Ni/NiO composite coatings prepared by sol–gel method

The Ni/C/NiO composite thin films have been prepared by one-step sol–gel method. The prepared samples were annealed at 450 °C with different holding times. When the metallic nickel nanoparticles were homogeneously dispersed in the composite, it is observed that both NiO and metallic Ni are surrounded by resident carbon. Comprehensive analysis techniques have been carried out in order to analyze the structural, optical, and solar- selective absorber properties of the composite. The main structure variations with various holding times are (i) the decrease in thickness and (ii) enhancement of metallic Ni nanoparticles size. The solar-selective absorber properties for one-layer Ni/C/NiO composite film annealed at 450 °C with 10 min of holding time show the optimal performance in the present work, exhibiting an absorbance of about 0.80 and an emittance of about 0.11, and capable of a good candidate as SSA for the low–middle temperature applications.