It is often found that the efficiency decreases because of the combining of electrons and positively considered holes at the junction. Since grain boundaries are the high energy zone, what methods can be applied to improve the efficiency of solar cells?
In a foundry the sand can be thermally reclaimed and reused after classification and removal of fines.
In a lab setting it is easier to use fresh sand at the pattern inter face and use mechanically recycled sand as back up
.If you are casting Al you can use an oil bonded sand and simply replenish the binder and oil each time.
Generally speaking "grain boundaries are the high energy zones" but that is not true for all the grain boundaries. For instance twin boundaries in FCC material are of significantly (orders of magnitude) lower energy than general high angle grain boundaries. By grain boundary engineering you try to increase the population of desired grain boundaries while decreasing the population of undesired boundaries. As an example, you can see how high electrical conductivity can be achieved in polycrystalline copper in here:
http://www.sciencemag.org/cgi/content/abstract/304/5669/422
Dear Anand,
The grain boundaries can be cosidered as surface crystallographic defects comprising a network of dislocations. They have effects on the electrical performance of the material. They increase the resistivity of the material because of the formation of potential barriers across the grain boundaries leading to additional scattering of mobile charge carriers across the grain. The other effect is that the defects in the grain boundaries acts a effective recombination centers.
The remedy to the mobility problem is to make the material in form of columnar structure where the grain boundaries lies in parallel to the flow of charge carriers.
The remedy for the high recombination rate at the grain boundary is to passivate the crystallographic defects by hydrogenation or prepherential doping. Hydrogenation is commonly used.
All these techniques are used in poly crystalline silicon solar cells.
Best wishes
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