What is the effect of increased doping density performance of ITO/InP solar cell?
Dear Khalil Ahmad,
Thank you foe inviting me to answer this question. The ITO/In P is a hetero junction solar cell where the the ITO acts as a wide bandgap window n-emitter layer and the InP functions as the main solar radiation absorber and substrate layer.The ITO is an intrinsically n-type metal like-with high electron concentration and so its carrier concentration is hardly to change with doping. Then it is the doping of the p-type In P substrate that can be varied to optimize the solar cell conversion efficiency.
Therefore, i will discuss the effect of the substrate doping concentration on the performance parameters of the solar cell.
As the doping concentration increases the mobility and the lifetime decrease and consequently the diffusion length is reduced. But practically the diffusion length remains greater than the active part of the substrate thickness. Accordingly, the collected photocurrent will be only very slightly reduced.
The main effect of the substrate doping is on the reverse saturation current.The doping concentration affects largely the conversion efficiency of the solar cells.As the doping density increases from relatively small values say 10^15 /cm^3, the reverse saturation current decreases leading to an increase in the open circuit voltage and consequently the conversion efficiency. This increase is sustained until the high doping effects begins to appear. The high doping effects are the reduction of the bangap and the the minority carrier life time. Both causes the reverse saturation current to decrease again after reaching a peak with the doping concentration in the substrate. The optimum substrate doping concentration amounts to about 2*10^17/cm^3. For more details refer to the link:http://scholar.google.com.eg/scholar_url?hl=en&q=http://www.researchgate.net/publication/224421373_Highefficiency_indium_tin_oxideindium_phosphide_solar_cells/file/72e7e518834b878a44.pdf&sa=X&scisig=AAGBfm3yEFfihcqL0bfqs-A3T8le2u4fAg&oi=scholarr&ei=IkwiUqLQCsSTtQb8uoHoDg&ved=0CDoQgAMoAjAA
Article High-Efficiency Indium Tin Oxide/Indium Phosphide Solar Cells
In terms of the sheet resistance and transmission parameters what would be desired for commercial applications?
Emitter layer doping actually reduce the sheet resistance and enhance conductivity or fill factor. But it reduces diffusion length or promotes defects that ultimately decreases the open circuit voltage.
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