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Fundamental Constraints Imposed by Thermionic Emission Barrier at the Hetero-Interface and by pn Junction Diffusion Barrier on the Fill Factor and Efficiency of SHJ Cells
M.Y. Ghannam, Y. Abdulraheem
Degradation, a-Si/c-Si Heterojunction, Fill Factor, Cell, Interface(s), SHJ, Hole Reflection
Silicon Photovoltaics
Subtopic: Heterojunction Solar Cells
Event: 33rd European Photovoltaic Solar Energy Conference and Exhibition
Session: 2AV.3.28
768 - 772
ISBN: 3-936338-47-7
Paper DOI: 10.4229/EUPVSEC20172017-2AV.3.28
0,00 EUR
Document(s): paper, poster


A model that links the relatively low Fill Factor (FF) in p+/n amorphous/crystalline silicon (a-Si:H/c- Si) hetero-junction solar cells (SHJ) with perfectly ohmic contacts to hole reflection at the hetero-interface under illumination is proposed. Such a reflection results from the partial emission and transport of holes imposed by the thermionic emission boundary condition at the hetero-interface. The non-emitted holes scatter back and diffuse towards the substrate, enhancing the cell forward current under illumination to levels well above the cell dark current leading to Fill Factor and efficiency degradation. The probability of hole reflection depends on the thermionic emission parameters and also on the diffusion barrier associated with the pn junction adjacent to the hetero-interface. Hole reflection is found to be particularly significant in cells with deficient active doping in a-Si:H. The model is supported by the results of AFORS-HET simulations at different operating temperatures.