Definition of antireflective coating (ar)

1) increases energy transmitted through optical surfaces by reducing Fresnel reflection losses.  The criteria for such a coating are that the refractive index of the material must be equal to the square root of the substrate index when the substrate is in air; also, the phase difference between the incident wave and reflected wave must be an odd multiple of pi.

2) Silicon is a shiny gray material and can act as a mirror, reflecting more than 30% of the light that shines on it. To improve the conversion efficiency of a solar cell, we want to minimize the amount of light reflected so that the semiconductor material can capture as much light as possible to use in freeing electrons.

Two techniques are commonly used to reduce reflection. The first technique is to coat the top surface with a thin layer of silicon monoxide (SiO). A single layer reduces surface reflection to about 10%, and a second layer can lower the reflection to less than 4%.

A second technique is to texture the top surface. Chemical etching creates a pattern of cones and pyramids, which capture light rays that might otherwise to deflected away from the cell. Reflected light is redirected down into the cell, where it has another chance to be absorbed.