3.2. Solar cell Construction & working

Summary

This lecture explores the construction and working of solar cells, fundamental units of solar photovoltaic systems. It explains the photovoltaic effect, where sunlight generates electrical current in solar cells made of semiconductors, typically silicon. The process involves doping silicon to create P-type and N-type semiconductors, forming a PN junction. When exposed to sunlight, photons excite electrons, creating charge carriers that flow through an external load, generating electrical energy. The lecture covers the generation of electron-hole pairs, how energy increases with more sunlight, and the typical output voltage of silicon solar cells, which ranges from 0.5 to 0.6 volts.

Takeaways

• 😀 Solar photovoltaic systems generate electrical energy directly from solar energy using the photovoltaic effect.
• 😀 The photovoltaic effect occurs when a photovoltaic cell generates voltage or electrical current when exposed to sunlight.
• 😀 Solar cells are made of semiconductors, typically silicon, and are the fundamental unit of solar photovoltaic systems.
• 😀 Semiconductor materials can be intrinsic (pure) or extrinsic (impure), with the latter being either P-type or N-type.
• 😀 N-type semiconductors have free electrons that can move to the conduction band when energized, allowing them to conduct electricity.
• 😀 Silicon solar cells are formed by doping a single silicon crystal with materials to create P-type and N-type semiconductors.
• 😀 A solar cell is essentially a PN junction diode, formed by combining P-type and N-type semiconductors.
• 😀 The N-type side of a silicon solar cell is doped with a pentavalent impurity, while the P-type side is doped with a trivalent impurity.
• 😀 When exposed to sunlight, photons excite free electrons, allowing them to move from the valence band to the conduction band, generating electricity.
• 😀 The output of a solar cell increases with more sunlight, as more electron-hole pairs are created, enhancing current flow and voltage generation.
• 😀 The maximum output voltage for a single-junction silicon solar cell is typically between 0.5 and 0.6 volts.

Q & A

What is the photovoltaic effect?

The photovoltaic effect is a phenomenon where voltage or electrical current is generated in a photovoltaic (solar) cell when it is exposed to sunlight. The energy from the solar radiation excites free electrons within the cell, leading to the production of electrical current and voltage.

What are the key components of a solar photovoltaic system?

The key component of a solar photovoltaic system is the solar cell, which generates electrical energy directly from solar energy using the photovoltaic effect. Solar cells are typically made from semiconductors like silicon.

How does a solar cell generate electricity?

A solar cell generates electricity by using the photovoltaic effect. When sunlight falls on the cell, photons excite electrons in the semiconductor material, creating free electrons and holes. These charge carriers move towards the P-side and N-side of the cell, respectively, and generate electrical current when metallic contacts are made.

What are the differences between P-type and N-type semiconductors?

P-type semiconductors are doped with trivalent impurities (such as boron), creating holes (electron deficiencies). N-type semiconductors are doped with pentavalent impurities (such as phosphorus), creating free electrons. The combination of these two types forms a PN junction in the solar cell.

What is the role of the depletion layer in a solar cell?

The depletion layer in a solar cell is formed at the junction of the P-type and N-type materials. It is where free electrons from the N-side and holes from the P-side combine, creating an electric field that helps in the movement of charge carriers (electrons and holes), facilitating the generation of electrical current.

How are electrons excited in a solar cell?

When sunlight (photons) strikes the solar cell, the energy excites the electrons in the semiconductor material, causing them to move from the valence band to the conduction band. This makes them free to move, contributing to electrical current.

What happens when solar radiation falls on a solar cell?

When solar radiation falls on a solar cell, it excites electrons from the valence band to the conduction band in the semiconductor material. This creates free electrons and holes, leading to a flow of charge carriers and generating electrical current.

What is the typical output voltage of a single-junction silicon solar cell?

The typical output voltage of a single-junction silicon solar cell is about 0.5 to 0.6 volts.

What is the importance of doping in the construction of solar cells?

Doping is crucial in the construction of solar cells because it creates the P-type and N-type semiconductors that form the PN junction. The doping process introduces impurities into the silicon crystal to control the flow of charge carriers, enabling the photovoltaic effect.

How does the generation of electron-hole pairs relate to the efficiency of a solar cell?

The generation of electron-hole pairs increases with the amount of solar radiation received by the solar cell. The more radiation incident on the cell, the more electron-hole pairs are generated, which results in higher electrical output and increased efficiency of the solar cell.