The photoconductive and photovoltaic (PV) transducers are the photoelectric transducers that convert light energy into electrical energy. Both are made up of semiconductor material which absorbs light energy and energizes the electrons of the material allowing them to flow through the material as an electrical current. Let us see the differences between photoconductive and photovoltaic (PV) transducers.
Definition of Photovoltaic Transducer :
A photovoltaic (PV) transducer or cell is a device that converts light energy into electrical energy through the photovoltaic effect. It is an active transducer, also known as a solar cell.
The output electrical energy produced is proportional to the intensity of light. The construction is similar to a p-n junction diode, with a thin layer of p-type semiconductor and a thick layer of N-type semiconductor.
When the cell is exposed to the sun, the negatively charged electrons in the cell get energized by absorbing small energize particles in the light called photons. This causes electrons to flow and thus electric current can be produced.
However the output of a single PV cell is low, but by connecting the number of cells in different combinations (series-parallel) required voltage and current can be obtained.
Definition of Photoconductive Transducer :
A photoconductive transducer or cell is a light-dependent resistor whose resistance can be controlled by light intensity. It is also known as a photoresistor made up of semiconductor materials like cadmium, selenide-lead sulphide, doped germanium, etc. The resistance of the photoconductive materials is a function of the incident electromagnetic radiation (light).
The working principle of a photoconductive cell or LDR or photoresistor is based on the photoconductivity or photoconductive effect. When enough amount of light intensity falls on the semiconductor material, the photons in light intensity energizes the electrons in the semiconductor material to jump from its valance band to the conduction band. This causes to decrease in resistance of the material, thereby increasing the current flow.
By incorporating an ammeter in the circuit, the change in the current due to change in resistance is measured and the attenuation of the light can be determined. It can also be used in light-controlled systems. It is a passive transducer since it requires an external source of electrical energy.
Difference Between Photoconductive and Photovoltaic Transducers :
| Photoconductive Transducer or Cell | Photovoltaic Transducer or Cell |
|---|---|
| When a photoconductive semiconductor element is subjected to radiation, its resistance changes (i.e., it decreases). Due to this, the flow of current through the cell increases. | When radiations fall on a photovoltaic cell, it generates a voltage whose value is proportional to the intensity of radiation incident on the cell. Thus, it converts electromagnetic energy into electrical energy. |
 |  |
| They are passive transducers. | They are active transducers. |
| They are highly sensitive to small changes in light intensity, they exhibit a high change in their resistance. | They possess a sensitivity of 1 mA/1m. |
| These cells possess a short response time of 10-100 µs. | These cells have a very short response time of 1-50 µs. |
| These cells do not respond to radiations having a wavelength less than 300 nm. Their spectral response extends from thermal radiation through visible, IR, UV up to X-rays and γ-rays. | The spectral response of these cells ranges from 200nm-2000nm. These cells are sensitive to α-rays, β-rays, γ-rays, and X-rays. |
| The characteristics of photoconductive cells are affected by temperature. | Photovoltaic cells are also stable but they are seriously affected by temperature. An increase in temperature leads to a rapid decrease in the output voltage of these cells, usually few mV/°C. |
| These cells are widely used in the measurement of radiant heat, quantitative spectroscopic measurements, and pyrometry. | They are used for energy conversion purposes. |
Therefore, a photovoltaic transducer can be used in generating electrical power. Whereas a photoconductive transducer can be used in light-controlled systems. A solar panel is made up of photovoltaic cells which are used to power various domestic, industrial and commercial applications.
The photoconductive transducer can be found in automatic street light control systems where the lights are turned on and off day and night automatically. It can be also employed in industries for counting the number of items moving on a conveyor belt.
