I am doing grain boundary simulation of multi-crystalline silicon based thin-film solar cells using TCAD Silvaco. On increasing number of grain boundaries in mc-Si region, Voc and FF are changing significantly but Jsc is not changing much. Please help me out to understand the physics behind it. Also, why interface defect density has high impact on Voc compared to Jsc but GB trap density affects Jsc more as compared to Voc?
Dear Muzaffar Imam ,
Do you have columnar structure? What is the thickness of the multicrysatlline layer? What is the of your junction? pn or pin one? It is clear that your semiconductor material parameters such that the photo generated electron pair holes will be collected before an appreciable recombination occurs.
The grain boundaries has more effect pn the dark current by increasing the reverse satiation current appreciably as the reverse saturation current is more sensitive to crystallographic defects than the Ish.
In order to verify my theory you need to calculate the reverse saturation current.
As the Js increases the Voc will be reduced. The fill factor also decreases because of increase in the series resistance and changing the squareness of the I-V curves. All this can you verify.
For more information about the effect of the grains on the solar cell please refer to the paper:Article Spectral response in polycrystalline silicon solar cells
Best wishes
Dear Myzaffar
You should show us the poly crystalline structure you simulate. Are grain boundaries horizontal or vertical ? Or random? I suppose you use
I suppose you use an artificial polycrystal with horizontally stacked grains (with vertical grain boundaries), so you get multiple cells connected in parallel with high internal series resistance between cells. The result is equivalent to almost the same Is but smaller Voc and of course smaller FF
Dear Muzaffar Imam
I agree with Abdelhalim abdelnaby Zekry's answer. I want to add some information his answer. Number of grain boundaries affect to recombination process and series resistance. Because, on the interface between two grains, the recombination centres are appeared. Increasing of number of grain boundaries is reason for increasing the number of recombination centres. We know that the open circuit voltage highly depend on the recombination rate. Besides, changing the number of grain boundaries can be reason for decrasing or increasing of fill factor depend on grain boundaries being vertically or horizontally.
Sincerely Jasurbek Gulomov
The different sensitivity of both FF and Voc compared to Jsc when the number of grain boundaries is increased comes from the following fundamental difference in the physical situation relevant for these quantities: The density of minority carriers being present in the solar cell is very low at Jsc but rather high at VMPP (relevant for FF) and Voc. As a consequence, recombination is nearly irrelevant for Jsc but highly relevant for FF and Voc. However, most relevant for Jsc is the absorption process, i.e., the light trapping and the spectral response.
Dear Prof. Abdelhalim abdelnaby Zekry,
Thank You for your response. I have taken horizontal and vertical GBs in the simulation of multicrystalline silicon. My structure is PIN, where P is microcrystalline silicon, I is multicrystalline silicon and N is microcrystalline silicon. Thickness of mc-Si have taken as 1.2 micron.
Dear Prof. Muhammad Hamza El-Saba,
Thank You for your response. I have taken horizontal and vertical GBs in the simulation of multicrystalline silicon. My structure is PIN, where P is microcrystalline silicon, I is multicrystalline silicon and N is microcrystalline silicon.
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