Solar Cell

SOLAR CELL

Principle

A solar cell is a basically a large area photo-diode which converts sunlight [solar energy] directly into electricity [Electrical energy], with larger efficiency, of photon absorption.

Fabrication

A solar cell is made up of a heavily doped 'p' and 'n' type materials grown over the substrate as shown in Fig. 4.14, with larger exposure area for the sunlight to pass through it.

Here, the thickness of the p-region and n-region is made small, so that the charge carriers generated in this region can easily diffuse to the junction. The 'p' and 'n' type material is connected to the load resistance R, through the ohmic contacts.

The symbol of the solar cell is as shown in Fig. 4.15.

Operation

1. The solar cell is exposed to the light without load resistance (R_L) and the photons are allowed to fall on the 'p' and 'n' type materials.

2. These photons collide with the valence electrons and eject it out from the parent atoms, thus electron-hole pairs are generated as shown in Fig. 4.16.

3. There electrons and holes quickly diffuses and reaches the depletion region as shown in Fig. 4.17.

4. Now, due to strong barrier field, the electrons (minority charge carrier) from 'p' type moves towards the 'n' side and similarly holes from 'n' type move towards the 'p'-side, as shown in Fig. 4.18.

5. As the p-n-junction diode is open circuited, the electrons and holes accumulate on either side of the junction, which gives rise to a open-circuit voltage (V₀) as shown in Fig. 4.19.

6. Now if a load resistance R_L is connected across the diode, then a reverse current I_R flows through the circuit as shown in Fig. 4.14.

7. Here, the magnitude of the current generated in the solar cell is proportional to the intensity of light falling on it.

Note: Large number of solar cells added togehter forms a solar panel.

Advantages

1. The energy used by solar cell is a renewable energy source i.e., sun.

2. These cells are eco-friendly and save electricity charges.

3. It is a pollution free device with higher efficiency.

4. Life time and durability is longer.

Disadvantages

1. Investment/installation cost is high.

2. It is a seasonal energy, which can't work under winter/rainy seasons.

3. The solar panels occupy more space during installation.

4. The electrical energy generated should always be converted from DC to AC, which is practically difficult.

Applications

1. Solar cells are used in the production of electricity to our daily needs.

2. Solar cells also provide electricity which may be used for commercial purposes.

3. They are used in artificial satellites and in space probes.

4. Solar panels are used in calculators, watches, street lights, toys etc.