The devices for harnessing solar energy are usually coated with:

Explanation:

1. Anti-reflective coating is applied to solar panels and other devices for harnessing solar energy to minimize the reflection of sunlight.
2. This allows more sunlight to be absorbed by the solar cells, increasing the efficiency of energy conversion.
3. It reduces the loss of solar energy that would otherwise be reflected off the surface of the device.

Additional Information

1.  Anti-glare coating: This is typically used in optical lenses, screens, and other surfaces to reduce glare, but it is not commonly used on solar energy devices.
2. Carbide coating: This type of coating is often used for hardening tools or surfaces exposed to wear and tear, but not typically used for solar devices
3. Titanium oxide coating: This coating is used for various applications, such as self-cleaning surfaces, but it's not the primary coating used to improve the efficiency of solar devices.