Page 72 - Applied Photovoltaics

Ȝ
d 0 (4.2)
1
4n 1
will, ideally, cancel the light reflected from the top surface by interference
effects from the light reflected at the coating-semiconductor interface, which
will be 180° out of phase (Heavens, 1955). This is illustrated in Fig. 4.2.

Figure 4.2. Use of a quarter wavelength antireflection coating to counter surface
reflection.

Reflection is further minimised if the refractive index of the antireflection
coating is the geometric mean of that of the materials on either side—glass
(typically) or air, and the semiconductor—that is, if

n n n (4.3)
1 0 2
Surface reflection can be reduced in this case to zero, as shown in Fig. 4.3.

Figure 4.3. Surface reflection from a silicon cell (n 2 = 3.8) in air (n 0 = 1) and under
glass (n 0 = 1.5) with an antireflection coating with refractive index and thickness
chosen so as to minimise reflection for 0.6 ȝm wavelength light.

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