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Co-evaporation of CIGS
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The CIGS layer (CuInGaSe2) is deposited by co-evaporating the elements in a very high vacuum (typically 10-6 Torr).
Each element Cu, In, Ga, Se is heated in a separate "effusion cell" and the cell temperature allow for a good control of the evaporation rate of each element.
Many processes exists where the elements can be evaporated altogether, or in different sequences. For example the so-called 3 step process involve evaporation of In,Ga,Se then Cu, Se then In, Ga, Se sequentially.
This is realized in a modified MBE equipment shown below :
— photo MBE —
Another setup is currently under construction to allow for the growth of much larger areas of material.
A complex arrangement of phases may be generated during the multi-step growth, which provide a suitable environment for the growth of CIGS grains.
Grain size appear to be a major parameter in the cell final quality, but this question is not clearly explained yet. Grain boundaries may play a role, which has been assessed as "beneficial" by some groups. Clearly a better understanding of the underlying physics still have to be established.
