I am fabricating Si solar cells with deposition of Ag (200 nm) by e-beam evaporation as the front electrode and Al (200 nm) as the back electrode by thermal evaporation. The sample was annealed at 500 C for 1 min after metal electrode deposition. However, everytime I get very low conversion efficiency due to the high series resistance. Does the series resistance depend on the thickness of the electrode ? If it is then thicker electrode is the only solution?? How can I solve this problem? Please help me.
There could be several options. Here is one possibility.
Silver is prone to oxidation giving silver oxide which can contribute to high series resistance. This problem can be overcome by improving the vacuum in the system, making silver film thicker or coating silver with a film of aluminum which is impermeable to oxygen.
Apply the Ag front contact silver thickness of about 1 micron by thermal evaporation under vacuum
Is annealing process running in oxygen free atmosphere? Because if it is, Ag and Al will oxidize. You could try replace it with N2 (cheapest gas for it). How low of resistance you need to achieve? Resistance values for metals not linear for thickness and you may need to increase both electrodes thicknesses. Another option is to do very thin coating of Au on top of electrodes, but it is expensive and Au most likely will not adhere well.
Thank you all for your nice suggestions. I'll try your suggested methods.
Dear Bhaskar Parida,
how high is the series resistance (per cm2) of the Si solar cells (under dark) ?
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