Silica Sol–Gel Coatings for Solar Panels: Drop Friction and Particle Adhesion

Soiling of solar panel surfaces reduces energy output and requires freshwater for cleaning. To address this challenge transparent, hydrophobic, and easy-to-clean silica-based coatings have been fabricated. Analysis of these coatings focused mostly on contact angle measurements, while drop mobility and particle adhesion─key factors for efficient soil removal─remain underexplored. To address this gap, here organically modified silicate coatings were synthesized by mixing tetraethyl orthosilicate (TEOS) with alkyl-trimethoxysilanes (alkyl-TMS) of varying alkyl chain lengths (methyl, <i>n</i>-propyl, and <i>n</i>-hexyl) and concentrations. The films showed high optical transparency (92%) and low surface roughness (0.3-1.0 nm). Increasing alkyl-TMS content and chain length increased surface hydrophobicity, leading to advancing contact angles up to 106°. By scanning drop friction microscopy and colloidal probe AFM, we quantified and correlated drop mobility and particle adhesion. A higher alkyl-TMS content led to a reduced drop friction force and reduced particle adhesion, although, mechanical robustness also decreased. Cleaning tests confirmed that coatings with lower friction and adhesion enable more effective soil removal.