NOVELTY - The porous sol-gel silica layer (2) comprises a series of closed pores (10-90%) with smallest characteristic dimension of greater than or equal to 20 nm. The porous layer is obtained with a solid blowing agent in a particulate form and is coated with a fluorinated organosilane or perfluoroalkylsilane. The pores have spherical or oval shape. The porous layer with pores of different sizes and proportions includes stack of porous layers with increased thickness. The porous layer has a refractive index of less than or equal to 1.1 at 600 nm.    USE - The coated substrate is useful as a transparent glass substrate for solar module (claimed). The porous sol-gel silica layer is useful as an anti-reflective coating on the glass substrate for windows, and as an optical splitter for multiple glazing or solar module.    ADVANTAGE - The porous sol-gel silica layer has improved optical, electrical and magnetic properties, and is durable and easy to implement.    DETAILED DESCRIPTION - The porous sol-gel silica layer (2) comprises a series of closed pores (10-90%) with smallest characteristic dimension of greater than or equal to 20 nm. The porous layer is obtained with a solid blowing agent in a particulate form and is coated with a fluorinated organosilane or perfluoroalkylsilane. The pores have spherical or oval shape. The porous layer with pores of different sizes and proportions includes stack of porous layers with increased thickness. The porous layer has a refractive index of less than or equal to 1.1 at 600 nm and is disposed on a sub-layer to be barrier with alkaline and to be adhesion promoter of silica or silicon oxide derivative such as silicon dioxide, silicon oxide under stoichiometric, oxycarbide, oxynitride or silicon oxycarbonitride. INDEPENDENT CLAIMS are included for:    (1) a coated substrate;    (2) a solar module;    (3) multiple glazing unit; and    (4) a method for fabricating the porous sol-gel silica layer on asubstrate.    DESCRIPTION OF DRAWING(S) - The drawing shows a solar module integrating a coated substrate of a porous layer.    Coated substrate (1)    Porous layer (2)    Glass (3)    Photovoltaic cell (4)    Solar module (10')    Lower face. (11)