In my simulation of a thin-film solar cell, I am trying to compare my results with experimental work. The best close results are obtained when I reduce the thickness of the absorbent layer. The best suitable results are obtained thickness of the absorbent layer is less than the thickness of the experimental absorbent. Can anyone please explain the reason behind this?
The absorption coefficient is different as you use a bulk value of material for calculations. The difference between bulk and think films maybe 10-15%, depending on a film's thickness and material. Besides, the composition of a film may show non-uniformity over the thickness.
Dear Adnan Hosen ,
welcome!
The minimum required thickness of the absorber is dictated by the absorption depth of the longest wave length. The other limiting factor is the diffusion length L of the minority carrier which are determined by the diffusion coefficient D and the minority carrier lifetime Tau such that L=sqroot D Tau.
The question now how much is the deviation between the two thicknesses?
There is always measuring errors and tolerances in the measurements.
Best wishes
Dear Dr. Abdelhalim abdelnaby Zekry Sir,
Thank you so much for answering the question. The minority carrier diffusion length was considered to be in the range 0.18 - 0.23 µm which leads to higher defect in the absorber. Can absorption depth of the longest wave length is different for the same material?
However, the deviation between the two thickness is about to 400 nm.
Dear Adnan Hosen ,
what is your thickness and their thickness?
What is the absorption thickness at the longest wavelength for this material.
If you diffusion length is about 0.18 um then it will not bring more gain if you increase the thickness of your cell even if the absorption depth at the longest wavelength is greater than this thickness.
Best wishes.
Dear Dr. Abdelhalim abdelnaby Zekry sir,
Thank you. That's the answer I was looking for!
However, Two different thickness is 0.8 µm and 1.2 µm, and 400 nm is the absorption thickness at the longest wavelength for the material.
Dear Adnan Hosen ,
welcome!
The photogenarated electrons and holes will be collected not only by the diffusion process but also by the built in electric field when the solar cell is a pin diode. The i-region will contain a built in electric field. This electric field will help in collecting the electrons and the holes in the i-region by assisting the diffusion process.
The collection process will be electric field assisted collection.
So it can have an effective diffusion length much greater than the 0.18 um.
I explained the such collection process in the paper at the link:Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells
In my opinion in spite of this paper is very interesting it did not fined its wide spread.
If you fine it okay please give your comment.
Best wishes
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