why do we want the photoelectric to occur in the junction region only in solar cell

Hi Rachana,

Solar or photovoltaic cells convert the sun's energy into electricity. They relay on the photoelectric effect:the ability of matter to emit electrons when a light is shone on it.

Silicon is a semiconductor and a key element of solar cells.

Sunlight is composed of miniscule particles called photons which radiate from sun.As these hit the silicon atoms of the solar cell, they transfer their energy to loose electrons, knocking them clean off the atoms.Freeing up electrons is however only half the work of a solar cell: it then needs to herd these stray electrons into an electric current. This involves creating an electrical imbalance within the cell, which acts a bit like a slope down which the electrons will flow in the same direction.

Creating this imbalance is made possible by the internal organisation of silicon.By squeezing small quantities of other elements into this structure, two different types of silicon are created: n-type, which has spare electrons, and p-type, which is missing electrons, leaving ‘holes’ in their place.
When these two materials are placed side by side inside a solar cell, the n-type silicon’s spare electrons jump over to fill the gaps in the p-type silicon. This means that the n-type silicon becomes positively charged, and the p-type silicon is negatively charged, creating an electric field across the cell. Because silicon is a semi-conductor, it can act like an insulator, maintaining this imbalance.
Hope this helps.