I want to increase porosity and roughness of the coating what will be its effect on light transmission and cleaning effect of solar PV glasss, or what are the limits
The roughness of surface can contribute to the extent of the diffused light, and rougher surface leads to increased light scattering or decreased transparency. Maximum scattering occurs when the roughness is comparable with the wavelength of the light. Light is scattered into different angles at each rough interface. This results in a prolonged average optical path-length and hence an enhanced light absorption in the layers. Scattered light beams fall on the interfaces non-perpendicularly which results in higher angular-dependent reflectances at the interfaces than in case of a normal incidence. Enhance reflections at internal interfaces lead to a more efficient light trapping which additionally increases absorption of light.
You can find more information in: Thin Solid Films 426 (2003) 296–304
If we consider the intensity of the incident beam to be "I" and that for the reflected beam to be "R", the transmitted beam to be "T", and the absorption portion to be "A", then transmitted beam intensity is T = I - (R + A). Obviously, R and A are impacted by the angle of incident, changes in the index of refraction at the interface, diffused reflectance due to surface roughness, and diffraction due to porosity and sample roughness as well as changes in the absorption coefficient of the coating used. Moreover, thickness of the film and how it is correlated with the wavelength (quarter- or half wavelength) also impact the transmission much like that done in anti-reflection coating.
Dear Kamran Alam ,
Hope you are well!
The roughness of a surface leads to light scattering. But if these structures are regular say have inverted pyramidal form then they can in the end effect reduce the reflectance from the surface. This exactly what is made when one structures the silicon surface. The porosity affects also the reflection coefficient and the refractive coeffect. Namely it may reduce the reflection coeffect leading to less reflectance of the incident light.
It will also reduce the refractive coefficient leading to near vertical light ray paths in the material.
If you made experiments please tell us about your findings.
Best wishes
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