NOVELTY - Forming a porous coating on a substrate, comprises: coating a substrate with a sol-formulation comprising a silane-based binder, silica-based nanoparticles, and an inter-particle interaction modifier for regulating interactions between the silica-based nanoparticles; and forming a gel on the substrate by drying the sol-formulation coated on the substrate.    USE - The method is useful for forming a porous coating on a substrate (claimed), where the coating is useful for manufacturing semiconductor device, solar cell, glass, and energy cell, and the substrate includes glass, silicon, metallic coated materials, or plastics.    ADVANTAGE - The method forms the porous coatings with good optical properties (e.g. a low refractive index) while maintaining good mechanical durability due to the presence of the inter-particle interaction modifier. The inter-particle interaction modifier increases the strength of the particle network countering capillary forces produced during drying to maintain the porosity structure. The anti-reflective coating reduces reflections of the incident light and permits more light to reach the thin film semiconductor film of the photovoltaic device and permitting the device to act more efficiently.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a sol-formulation for forming a sol-gel, comprising an alcohol containing solvent, an acid or base containing catalyst, a silane based binder, silica-based nanoparticles, and an inter-particle interaction modifier for regulating interactions between the silica-based nanoparticles; and    (2) a method-1 of making a sol-formulation, comprising mixing a silane-based binder, an acid or base containing catalyst, silica-based nanoparticles, an alcohol containing solvent, and an inter-particle interaction modifier for regulating interactions between the silica-based nanoparticles to form a reaction mixture by at least one of a hydrolysis and polycondensation reaction.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic diagram of a porous coating on a glass substrate.    Glass substrate (200)    Porous antireflective coating. (210)