# Scratch Resistant Antireflective Coating

## Problem

Glass coated with antireflective films is used as the outer protective layer of solar panels used in a photovoltaic system. Structural damage to the antireflective coating on the glass will lead to the loss of optical transmission and solar energy efficiency.

## Why it Happens?

Solar power plants are commissioned in a sunny and dusty environment. The wind carries coarse dust particles (0.12 to 0.50 mm) which can impact the antireflective coating on the glass. The kinetic energy of these dust particles is converted into plastic deformation and fracture of the coating and glass. As a result, the diffusion of light will be increased rather than its transmission into the photovoltaic cells.

## Solution

The glass was coated with a protective multilayered coating (Table 1). The coating was then scratched using a diamond indenter of 0.20 mm in diameter. Scratch test parameters are as listed in Table 2. Multiple scratches on the glass samples are as illustrated in Figure 1. Friction profile showed a failure of the coating at a normal force (or adhesion force) of 50 N (Figure 2). The accuracy of determining such a failure was at 2% (Figure 3). Overall, a method to accurately test the failure of antireflective coating used in solar power plants is demonstrated.

Table 1. Composition and thickness of the deposited layers.

Coating Thickness [µm]
TiO2 10
SiO2 45
TiO2 45
SiO2 10
TiO2 45
SiO2 90

Table 2. Test parameters used in a Ducom Scratch Tester.

Parameter Unit Value
Load N from 20 to 70 (ramp)
Scratch velocity mm/s 1
Stroke length mm/s 2
Tested samples - 15

Figure 1. Scratches on antireflective coating on a glass sample.

## Results

Figure 2. Real time changes in friction force over a stroke length during a ramp load test. It has 30 test results from 15 glass samples with same coatings.

Figure 3. Measured adhesion force (or load at failure) for 30 test samples.

This information has been sourced, reviewed and adapted from materials provided by Ducom.