Opto-electronic (Photo electric) Transducers

Transducers which converts light energy into electrical energy is known as Photoelectric transducers. There are different types of photoelectrical transducers:

1. Photoemissive Cell
2. Photoconductive Cell
3. Photovoltaic Cell

Photoemissive Cell or tubes

A photoemissive cell consists of an Anode, cathode, glass envelope and connecting pins. 

The anode is a rode and the cathode is a curved plate coated with a photoemissive material like Cesium antimony. Currents produced across anode and cathode.

Both anode and cathode are sealed within an evacuated envelope.

When a beam of light falls on the cathode, electrons are released from it, which are drawn towards the anode. The anode is maintained at certain positive potential. This gives rise to a photoelectric current.

The current produced across the anode and cathode is proportional to the intensity of the incident light on the cathode. The spectral response also depends on the nature of material coating in the cathode.

Photoconductive Cell

Photoconductive cell converts solar radiation into conductivity.

The resistance of the photoconductive material change when a beam of light is incident on it. Basically, the materials are Ge, Si, Cadmium Selenide.

When photoconductive cell got sufficient sunlight then its conductivity increases and it works like a closed switch. If there is no light then the cell works as an open switch.

Photovoltaic Cell

A photovoltaic cell or solar cell is an active transducer, which generates electricity when irradiated by sunlight.

A P-type silicon and N-type material are diffused to form a photovoltaic cell When a semiconductor material is exposed to light, photons of the light ray are absorbed by semiconductor crystal which causes significant number of free electrons in the crystal, this phenomenon is called photovoltaic effect.

The photovoltaic effect is the basis of generation of current across the semiconductor. Current generated is taken across the PN junction, where P is the positive and N negative terminal.