Question

How does a photovoltaic cell generate electricity? How thick is the depletion width in a silicon solar cell? How can you calculate it?

Answer 1

In the simpler terms if you break down the terms of photovoltaic cell it means " cell that converts Photon( Scientific term for light ) into electricity.

Let just look into the construction of cell to understand its working:

Principle :

Photovoltaic cells are made up of special type of material "semiconductors " - silicon which is currently widely used material in PV(short-form for Photovoltaic cell). It works on the principle that when a sun light carrying a enery falls on a cell, some atoms in the cell absorbed the energy and this absorbed energy is taken up by loosed electrons which free and flow freely and this flow of electrons consist a electricity.

Working :

silicon consist of 14 electron hence if you see the electronic configuration of the atom it consist of 4 free electrons in the last orbit . and it always try to fill that up and hence it bonds with other 4 silicon atoms and forms a strong structure. In this strong structure it does not conduct but when it is doped with other atoms such as phosphorous conduct elctricity. which is known as P-type doping . Now on crytalline structure of silicon one atom is replaced by one atom of phosphorous and Phosphorous contains 5 free electrons out of which 4 bonds with the silicon and 1 is free flowing which conducts electricity.

Now this free electroon absorbs energy from photon and freely conduct electricity. At top and bottom metal contactors are placed which conduct the free electrons.

PV - silicon cell thickness :

A optimum solar cell thickness about 100 micrometer. However thickess between 200 to 450 micrometer are typically used for practically used.

Calculation :

It is calculated by asssuming certain assumptions and then solving the "Poisons Equation " to get the optimum thickness for the PV cell.