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f-alpha.net » Physics » Semiconductor Physics » Photovoltaic Effect » Let's go... » Experiment 3 - np-Junction

Experiment 3 - The np-Junction of the Solar Cell

The solar cell consists of a very thin layer of n-type silicon (about 1 μm) on a thicker layer of p-type silicon (about 0.5 mm).

In the resulting np-junction the free electrons and holes are migrating (diffuse). Thereby they form electron-hole pairs.

Illustration diffusion of the free charge carriers (electrons in blue and holes in red) in the np-junction. (Enlarge)

This has some important consequences...

  • In the junction, there are only very few free charge carriers. One speaks of a of a charge-depleted layer.
  • The n-layer is charged positive (positive space charge) and
  • the p-layer is charged negative (negative space charge).

Illustration Illustration electron-hole pairs in the np-junction. (Enlarge)

The space charge is very important, as it provides the "motor" for the photovoltaic effect and hence the solar cell...

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