The middle glass between the two cells the upper and the lower cells is a supporting glass for the lower thin film solar cell. It is an optical coupling layer only. So, you have to connect the two cells electrically by by vias across this glass layer or through the side wall metallization of the glass.
Here the middle galss can be consider an optical transparent medium.
Thick substrates with a few millimeters thicknesses can be modeled as a thin layer with a micron thickness by applying one of two approaches. The phase-matching approach, or the phase-elimination approach. You can find more details in these papers.
Actually, Thin film solar panels often have a standard glass because they are cheap.
In crystalline solar panels, a 3 to 4mm thick solar glass is often used. The thicker the glass in the crystalline solar panels, the more stable are they. Solar panel glass on cheaper modules may be as thin as 2.5mm.
The solar panel glass (in the crystalline solar panels) is not standard glass it has a rough surface. This is necessary to make the EVA film bond well to the solar panel glass during the lamination process. Smooth glass can lead to the delamination.
The glass which is used in solar PV panels is of immense importance as it can make a big difference to the solar panel efficiency and therefore the yield of the solar PV system.
Solar panel glass should ensure a high solar radiance transmittance
The primary purpose of solar panel glass is to transmit as much sunlight as possible into the module.
A highly transmissive solar panel glass has a direct positive effect on the performance and yield of the solar PV panels.
This link will help you for more information related to your question,
The middle glass between the two cells the upper and the lower cells is a supporting glass for the lower thin film solar cell. It is an optical coupling layer only. So, you have to connect the two cells electrically by by vias across this glass layer or through the side wall metallization of the glass.
Here the middle galss can be consider an optical transparent medium.
Sir do you have any silvaco tcad code so that it can be more clear to me it is still a little bit unclear that how to write, what material to be taken and how to metallize it as you told so
If you are talking about the interlayer between the two junctions [ 4 terminal configuration of the tandem solar cell], then you need to include it in an optical simulation as it causes some reflection losses. Maybe the following thesis can help.
The two cells here can be considered as two separate cells. They are optically coupled by the intermediate thick glass layer. So, they can be separately simulated with each cell having its own I-V characteristics. Optically
The transmitted light from the upper cell is made to enter the lower cell.
To let the two cell working in tandem then one has to make their shortcircuit current equal.
This can be accomplished by adjusting the thickness of the absorber of the upper layer just to pass a part of the incident solar radiation making equal shortcircuit current in the cells.
Then what do you make here is the optical analysis. In optical analysis the material parameters of interest is the dielectric constant and the absorption coefficient of the material. By doing the optical analysis you will be interested in the light passing from the upper cell to the lower cell.
The method is that you decrease the upper solar cell thickness and continue calculating the upper and lower cell currents till they get equal.
The advantage of the four terminal tandem cells is that they only optically coupled. So, one do not need to consider their electrical coupling.
Because the two cells can be considered as two separate cells, You can take the Glass region in Silvaco tool as an air (or Transparent layer with low reflection) use an accurate thickness of this layer.
I would suggest looking for some good examples in the SILVACO package. In attached I am sending to you a SILVACO code for Tandem solar cells that may be useful to you.