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

## TL;DR

This paper introduces silica-based coatings for solar panels that reduce soiling and cleaning needs by minimizing drop friction and particle adhesion.

## Contribution

The study introduces and evaluates organically modified silicate coatings with varying alkyl chain lengths to improve solar panel cleanliness and efficiency.

## Key findings

- Coatings with higher alkyl-TMS content showed increased hydrophobicity and reduced drop friction and particle adhesion.
- Lower friction and adhesion in coatings led to more effective soil removal during cleaning tests.
- Optical transparency remained high (92%) with minimal surface roughness (0.3–1.0 nm).

## Abstract

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, n-propyl,
and n-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.