Photoelectric Cell are of 3 types:

1. Photo emissive cell

2. Photo conductive cell

3. Photo voltaic cell

The cell in which energy of the photons if incident light is utilized to obtain photoelectrons and hence the photoelectric current is called photo emissive cell

It works on the principle of photoelectric emission-

(ii) PHOTO CONDUCTIVE CELL:

When a potential difference  of 100 V is applied across the transparent film

And the metallic layer of Fe is kept at the bottom. An electric current flows in the external circuit which can be enhanced by falling the light rays on the transparent film.

(iii) PHOTO VOLTAIC CELL:

The cell consists of a metallic layer of Cu on which semi conducting layer of Cu₂O₂ is made. This layer is covered by a thing transparent film of silver when the sunlight falls on the semi conducting layer. Photo electrons are ejected from the surface due to which Potential Difference is developed between the upper 2 layers.