I have used Aluminum as a back contact for CdTe solar cell, but the thing is Al acts as a schottky barrier at room temperature,If anybody knows the optimization procedure please share me the reference.
Thank you.
Ideally, you would want your back contact material to have a similar or higher work function than your CdTe layer to avoid the formation of a schottky barrier.
In your case, the formation of the schottky barrier can occur due to multiple reasons, including the experimental details of your CdTe deposition as well as treatment before the AL deposition. There are several approaches to reduce the barrier height. One is the so called NP etching to form a Te rich p+ layer before depositing a metallic back contact. There is a lot of in depth literature on this topic. For a good overview I would suggest Chalcogenide Photovoltaics from Scheer and Schock. I hope that helps.
Raghu,
In general, it depends on whether the CdTe is p-type or n-type. Many of the CdTe solar cell polycrystalline layers are weakly p-type with a hole concentration of 10^13 to 10^14. In addition the surface of CdTe is partially pinned, so even if you could find a high work function material it probably wouldn't make a low resistance contact. In essence you need to form a low resistance contact before applying the aluminum or whatever other kind of metal.
I would suggest downloading my paper "Exploring Back Contact Technology to Increase CdS/CdTe Solar Cell Efficiency" from ResearchGate which is kind of an overview of the subject
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Alan gave you the best advice. If you are talking about n-type crystal you can make ohmic contact with Al by annealing in reducing environment. If p-type or near-intrinsic you need an interlayer (typically containing Cu). Please clarify what type of CdTe you are working with (thin film, crystal, n-type, p-type?)
Best results to form an ohmic contact for CdTe are usually obtained depositing a small layer (2-4 nm) of Cu. The typical annealing temperature is 200 C for 20 min. This results in CuTe Cu2Te compounds formation. To etch the CdTe surface before of the Cu deposition by Br-MeOH or NP increases the Te ions relative concentration and then the reactivity of the surface. The presence of these compounds explains better the ohmic contact.
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