In solar cells a silicon solar cell (refractive index=3.5) is coated w...
In solar cells a silicon solar cell (refractive index=3.5) is coated w...
Explanation:
When light waves pass from a medium with a high refractive index (such as silicon) to a medium with a lower refractive index (such as air), a portion of the light is reflected. This results in a loss of energy and reduced efficiency in solar cells. To minimize reflective losses, a thin film of a material with a lower refractive index (such as silicon monoxide) is coated on the surface of the silicon solar cell.
Path Difference:
When light waves reflect off a surface, they undergo a path difference. The path difference is the difference in the distance travelled by the reflected wave and the incident wave. To minimize the reflection, the path difference should be equal to half the wavelength of the incident light (λ/2).
∆x=2t:
The path difference can be calculated by considering the distance travelled by the reflected wave inside the thin film (2t) and the distance travelled by the reflected wave in the medium outside the film (air). Since the light travels twice the thickness of the thin film inside and outside, the path difference is equal to 2t.
Minimum Thickness Calculation:
Using the formula for path difference, we can calculate the minimum thickness of the silicon monoxide film that minimizes reflection at a wavelength of 550 nm.
Path difference = λ/2
λ = 550 nm (given)
Path difference = 550/2 = 275 nm
The refractive index of silicon is 3.5 and the refractive index of silicon monoxide is 1.45. Using the formula for the optical path length,
Optical path length = thickness × refractive index
For the reflected wave, the optical path length inside the silicon monoxide film and in the air must be equal to the path difference.
2t × 1.45 + 2t × (1/1) = 275 nm
Solving for t, we get:
t = 47.6 nm (approximately)
Therefore, the minimum thickness of the silicon monoxide film that produces the least reflection at a wavelength of 550 nm is approximately 47.6 nm.
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