Solar Cells From Polycrystalline Cast Si

Here is a typical poly-Si slice and a solar cell made from a similar slice. The dimensions are 10 cm x 10 cm.
While the poly-Si slice is relatively fine grained (probably form about 1993), the solar cell (from about 1998) shows coarser grain structures - demonstrating the progress made in casting technology
Solar poly-Si and solar cell
How good are polycrystalline solar cells? Not too bad, actually, but not as good as solar cells from very good single crystals.
Below are four color coded maps showing essential parameters lod solar cells locally. These maps are not easy to obtains; they result from a new technique, developed by a university of Kiel research group, called "CELLO" (short for "Cell Local"). More details via the link. The parameters measured are:
"Current", meaning the maximum (short-circuit current) that can be drawn from a pixel.
"Voltage", meaning the voltage a pixel would produce if it would be an isolated cell by itself.
"Series resistance", essentially meaning the ohmic resistance that would be found in an equivalent circuit for one pixel
"Process defects", a lumped parameter that displays serious local problems like, e.g., locally leaking pn-junctions.
Peformance of poly-Si solar cell
The progress made with multi-crystalline Si solar cells in comparison to competition is shown in the picture below
Dvelopment of solar cell efficiency

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go to 3.1.3 Mechanical, Thermal and Other Properties

go to 3.2.2 Polycrystalline Silicon

© H. Föll (Semiconductor - Script)