Compare the operation of a photovoltaic solar cell with that of a photoconductive cell.
The correct answer and explanation is :
A photovoltaic (PV) solar cell and a photoconductive cell both operate based on the principle of converting light energy into electrical energy, but their mechanisms differ in how they generate and use electricity.
Photovoltaic Solar Cell:
A photovoltaic solar cell operates on the photovoltaic effect, where light photons are absorbed by a semiconductor material (typically silicon). When light strikes the material, it excites electrons, knocking them loose from their atoms. This creates electron-hole pairs (free electrons and positive “holes”). The solar cell has an internal electric field (typically created by the p-n junction in silicon cells), which separates these charges. The electric field pushes the electrons toward the negative terminal and the holes toward the positive terminal, creating a direct current (DC) electrical flow. This current can then be used to power electrical devices or be stored in batteries.
Photoconductive Cell:
A photoconductive cell, on the other hand, operates on the photoconductivity principle. In these cells, the material (often cadmium sulfide or other semiconductors) becomes more conductive when exposed to light. Under normal, low-light conditions, the material has a high resistance, meaning it doesn’t conduct electricity well. However, when light hits the material, the energy from the photons excites electrons, increasing their movement and, thus, the conductivity of the material. This results in a decrease in resistance, allowing current to flow. The amount of current produced depends on the intensity of the light, but unlike photovoltaic cells, this current does not form a permanent, usable electrical output until the light is shining on the material. Photoconductive cells typically generate very small currents and are mainly used in applications like light sensors, exposure meters, or in some cases as part of solar-powered devices.
Key Differences:
- Energy Conversion: Photovoltaic cells convert light into a usable direct current (DC) through the movement of charge carriers, while photoconductive cells change their conductivity in response to light, generating a variable current.
- Application: Photovoltaic cells are used in energy generation, powering systems like solar panels, whereas photoconductive cells are used for light detection, sensors, and smaller electronic devices.
- Output: PV cells provide a continuous and stable electrical current, while photoconductive cells typically provide an intermittent current that varies with light intensity.
In conclusion, photovoltaic cells are used for energy generation, while photoconductive cells are more useful for detecting light and measuring its intensity.