A depletion zone, also known as depletion region or a space charge region, is such a zone where there are no free carriers. To learn this more, you need to understand the underlying principles of solar cells.
Inorganic solar cells are primarily composed of doped silicon materials, though nanomaterials can now be employed as well. P-type and n-type silicon are typically paired up to form junctions in solar cells. For comparison, n-type doped materials have atoms with an extra electron in their atomic lattice while p-type doped materials have atoms with one less electron. For n-type and p-type materials, a result of this is the creation of extra electrons and holes, respectively.
The energy conversion mechanism involves both charge carriers. The junctions in a photovoltaic cell can only be built from specific materials because they must be able to undergo the photoelectric effect, which is the formation of a voltage in the presence of light.
These two doped silicon materials come together to form a semiconducting junction when they are placed close to one another. An abundance of holes can be found on one side of this junction, and an abundance of electrons can be found on the other.
The depletion zone, an electrically neutral region sandwiched between these two charge carrier regions, serves as the junction interface between them. When the photovoltaic cell receives no sunlight, the depletion zone develops.
Some of the electrons and holes interact with one another and come together to form the depletion zone. In order to keep the other charge carriers apart from one another, both charge carriers join to produce a neutral species.
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The neutral zone creates an internal electric field that keeps the two charge carrier areas from fully mixing with one another in the solar cell in addition to separating the charged species.
This is crucial because a complete collision between these two zones would produce an electrically entirely neutral substance that would not function as planned.
This is due to the fact that an electrically neutral material would not produce an electrical current, and the migration of these charges in response to light stimulation is what makes solar cells function and produce photovoltaic energy.