There are many effective technologies that have been developed in the field of renewable energy. In this context, this study covers a selective coating used in the photo-thermal conversion on macro-scale devices. The objective of this work is to optimize a silicon-based paint layer for solar application in the low temperature range (T<80℃) where the optimization thickness is found 21 µm. In order to apply the optimization layer (21 µm) in the solar devices that work in the medium temperature range (80℃<T<200℃), we propose to deposit a thin film of indium oxide using an ultrasonic spray chemical vapor deposition USCVD process to obtain finally a bilayer structure (silicon-based paint Thickness-Insensitive Selective Solar TISS / In2O3). The obtained bilayer structure was tested and characterized using spectroscopy of UV-VIS and IR, the last one was used in two modes: specular and diffuse reflection. The structural properties were investigated using the X-rays diffraction (XRD) and the morphological character was analyzed using Scanning Electron Microscope (SEM). In addition, the global results denote that the deposition of In2O3 layer improves the reflection capacity of the optimization layer (21 µm) from 8 to 11 in the NIR range.