# Anti-Reflection Coatings

Bare silicon has a high surface reflection of over 30%. The reflection is reduced by texturing and and by applying anti-reflection coatings (ARC) to the surface1. Anti-reflection coatings on solar cells are similar to those used on other optical equipment such as camera lenses. They consist of a thin layer of dielectric material, with a specially chosen thickness so that interference effects in the coating cause the wave reflected from the anti-reflection coating top surface to be out of phase with the wave reflected from the semiconductor surfaces. These out-of-phase reflected waves destructively interfere with one another, resulting in zero net reflected energy. In addition to anti-reflection coatings, interference effects are also commonly encountered when a thin layer of oil on water produces rainbow-like bands of color.

The thickness of the anti-reflection coating is chosen so that the wavelength in the dielectric material is one quarter the wavelength of the incoming wave. For a quarter wavelength anti-reflection coating of a transparent material with a refractive index n1 and light incident on the coating with a free-space wavelength λ0, the thickness d1恒大彩票网址是多少 which causes minimum reflection is calculated by:

## ARC Thickness

ARC Thickness Calculator

Optimal ARC thickness, d1: 0.75 μm

Reflection is further minimized if the refractive index of the anti-reflection coating is the geometric mean of that of the materials on either side; that is, glass or air and the semiconductor. This is expressed by:

## ARC Refractive Index

ARC Refractive Index Calculator

Optimal refractive index of ARC, n1: 2.2913

For the reflectance at normal incidence we define a series of parameters: r1, r2, and θ. The surrounding region has a refractive index of n0, the ARC has a refractive index of n1 and a thickness of t1, and the silicon has a refractive index of n2.

## ARC Substrate Reflectivity

13

thickness =

10200

The graph shows the effect of a single layer anti-reflection coating on silicon. Use the sliders to adjust the refractive index and thickness of the layer. For simplicity this simulation assumes a constant refractive index for silicon at 3.5. In reality the refractive index of silicon恒大彩票网址是多少 and the coating is a function of wavelength.

Comparison of surface reflection from a silicon solar cell, with and without a typical anti-reflection coating.