What thickness (or range of thickness) will be beneficial for MaF2 anti-reflection coating over SLG glass substrate for CdTe based Superstrate solar cell? What can be the possible effects of ARC thickness variation?
Hello Mahabub,
the thinnest layer depends on the wavelength L and the refractive index of the ARC-layer n. For vertical incidence you have the thickness do
do = L/(4n)
The next steps are d = do*k with k = 1,2,3....
This formulae follows from the interference of light in the upper layer. The single layer can be substituted by an interference filter. But the disadvantage is the high selectivity for a single wavelength.
Yours
R. Mitdank
Dear Mahabub,
Completely agree with what has been said above by Rüdiger Mitdank and wish to add the following:
A Mono ARC (MARC) is the minimum requirement for any solar cell. It is not only a matter of thickness but also of refractive index of both the substrate and the MgF2 coating. As the optimum transmittance is observed at a film thickness equal to one quarter of the wavelength of the incident light, these systems are referred to as λ/4 layers.
If an optimal thickness of ARC is inserted between the glass (G) and the environment (air), the minimum reflectance is given by the following equation : R = [(nARC ^ 2-n_ air* n_G) / (〖n_ARC〗 ^ 2 + n_ air* n_G)] ^ 2 Where n_ARC is the refractive index of the MgF2 (close to 1.36). To obtain zero reflectance at a wavelength, the value of n_ARC should be: n_ARC = (nair × nG)^1/2 The thickness of the ARC (d_ARC) must meet the optical thickness requirement of a quarter (1/4) of the wavelength: d_ARC = λ0 / (4 × n_ARC) As λ0 is the wavelength where the reflectance is zero or minimal.
for further details, take alook to the follwoing article :
Article Sol-Gel Processing of MgF2 Antireflective Coatings
I agree with Rüdiger Mitdank comment. Though i have not studied
minimum possible thickness of ARC layer of MagF2 coating but TiO2 for metal oxide heterojunction i have investigated and found the thickness 20-50 nm.
The issue of the antireflective coating has been studied intensively in the literature specially for silicon solar cells and you can apply the gained rules to other materials as the colleagues invoked above. For the antireflective coating design please refer to the book chapter: https://www.researchgate.net/publication/323309527_Solar_cells_and_arrays_Principles_analysis_and_design
There is lambda /4 n concept and in addition the rule concerns the n antireflective coating= sqroot of ( nair x n substrate) where n is the refractive index of the stacked layers for matching and enhancing the transmission.
Best wishes
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