All Answers Must Have 5–7 Sentences Each Written In Your Own

All Answers Must Have 5 7 Sentences Each Written In Your Own Words1

What are semi-conductors? Give two examples.

Semi-conductors are materials whose electrical conductivity falls between conductors like metals and insulators such as rubber. They have the ability to conduct electricity under certain conditions while blocking it under others, which makes them essential in electronic devices. The conductivity of semi-conductors can be modified by adding impurities—a process called doping. Common examples of semi-conductors include silicon and germanium. These materials are fundamental components in most modern electronic devices, including computers and smartphones.

What is Fermi distribution?

The Fermi distribution describes the probability that an electron state at a particular energy level is occupied at a given temperature. It is a statistical function derived from quantum mechanics that helps explain the behavior of electrons in metals and semi-conductors. The distribution indicates that at absolute zero, all states below the Fermi energy are filled, and those above are empty. As temperature increases, electrons gain thermal energy, allowing some to occupy states above the Fermi level. This concept is crucial in understanding electrical conductivity and the behavior of electrons in different materials. It helps in predicting how electrons will respond under various thermal and electrical conditions.

What are p-type and n-type semiconductors?

P-type and n-type semiconductors are types of doped materials used to control electrical conductivity. P-type semiconductors are doped with elements that have fewer valence electrons than the base material, creating holes or positive charge carriers. N-type semiconductors are doped with elements that have more valence electrons, providing additional free electrons or negative charge carriers. These doped regions form the basis for creating electronic devices like diodes and transistors. The imbalance of charge carriers in these materials allows for the flow of current when external voltage is applied. They are fundamental in designing and functioning of various electronic and optoelectronic components.

Explain a process for fabricating p type and n type semiconductors.

The fabrication of p-type and n-type semiconductors involves the process of doping. For p-type semiconductors, the base material such as silicon is doped with elements like boron, which has fewer valence electrons. This creates a surplus of holes, increasing conductivity. For n-type semiconductors, the process involves doping silicon with elements like phosphorus that have extra valence electrons, resulting in free electrons. The doping process typically involves thermal diffusion or ion implantation, followed by annealing to activate the dopants. These doped regions are then selectively processed to create p-n junctions. Proper control during fabrication ensures the desired electrical properties for electronic applications.

What is p-n junction?

A p-n junction is a boundary or interface between p-type and n-type semiconductors within a single crystal. It is a fundamental building block of many electronic devices like diodes, transistors, and solar cells. When p-type and n-type materials are joined, electrons from the n-side diffuse into the p-side and holes from the p-side diffuse into the n-side, creating a depletion zone devoid of free charge carriers. This zone acts as a barrier that influences electrical conduction and allows current to flow in one direction only, making it rectifying. The p-n junction underpins the operation of semiconductor devices and their applications in electronics. Its behavior is crucial for controlling electrical flow in various circuits.

What is the difference between photoelectric effect and photovoltaic mechanism?

The photoelectric effect involves the emission of electrons from a metal surface when it is exposed to light of sufficient frequency, leading to a current flow. It requires a metal surface and typically involves electrons being ejected into a vacuum or surrounding medium. In contrast, the photovoltaic mechanism refers to the conversion of sunlight directly into electrical energy within a semiconductor material, such as silicon cells. This process does not involve electron ejection but the generation of electron-hole pairs that produce a current when separated by an electric field. The photoelectric effect is mainly used in photodetectors, whereas the photovoltaic effect is the principle behind solar cells. Both phenomena depend on the energy of incident photons but operate through different physical processes.

How are batteries different from photo voltaic cells?

Batteries are electrochemical devices that store chemical energy and convert it into electrical energy through chemical reactions. They provide a stored energy source that can be used repeatedly after recharging. Photovoltaic cells, on the other hand, convert sunlight directly into electricity using the photovoltaic effect in semiconductors. Unlike batteries, solar cells do not store energy; they generate power when exposed to sunlight. Batteries typically have a limited number of charge-discharge cycles, whereas solar cells can function for decades with minimal maintenance. Each technology serves different roles but can be integrated in renewable energy systems.

What are different technologies used for improving efficiency of a photo voltaic cell?

Efficiency improvements in photovoltaic cells involve several advanced technologies. Texturing the surface of solar cells reduces reflection and increases light absorption. Anti-reflective coatings further enhance light capture. Employing passivation layers minimizes surface defects that impede electron flow, thereby improving efficiency. Use of better semiconductor materials such as perovskites or multi-junction cells allows for broader spectral absorption. Concentrated photovoltaic systems use lenses to focus sunlight onto smaller, high-efficiency cells. Additionally, improving electrical contacts and reducing resistance within the cell can significantly boost overall efficiency. Continuous research is focused on novel materials and device architectures to make solar cells more efficient.

What is a multi-junction cell? Explain how the efficiency of a cell is improved using this technique.

A multi-junction cell consists of multiple layered semiconductor structures, each designed to absorb a different portion of the solar spectrum. By stacking different materials with varied band gaps, these cells efficiently utilize a broader range of sunlight compared to single-junction cells. The multiple layers allow for higher voltage and increased energy conversion efficiency. The design reduces the thermalization losses typical of single-junction cells, as photons are absorbed at their respective energy levels. This layered approach has yielded efficiencies exceeding 40%, making multi-junction cells highly suitable for space and high-concentration applications. Overall, this technique harnesses the full potential of incident sunlight, dramatically improving the power output of solar cells.

What is Shockley-Queisser limit?

The Shockley-Queisser limit defines the maximum theoretical efficiency of a single-junction solar cell under standard test conditions, approximately 33.7%. It considers fundamental physical constraints, including thermodynamics, photon absorption, and radiation losses. The limit arises because photons with energy below the band gap are not absorbed, while those with higher energy lose excess energy as heat. This limit sets a benchmark for the maximum efficiency achievable without multi-junction or advanced materials. Ongoing research seeks ways to surpass this threshold by developing innovative device architectures or multi-junction cells. Achieving efficiencies close to this limit is essential for making solar power more competitive and sustainable.

Diagram and Explanation of Solar-Electricity Generation in a p-n Junction Cell

The operation of a solar cell hinges on the p-n junction's ability to convert light into electricity. When sunlight strikes the cell, photons with sufficient energy excite electrons in the semiconductor, creating electron-hole pairs. The built-in electric field at the p-n junction directs electrons toward the n-side and holes toward the p-side, separating charges and generating an electric current. The flow of electrons through an external circuit delivers usable electrical power. During this process, the voltage across the terminals depends on the light intensity and the quality of the semiconductor material. In essence, the p-n junction acts as a diode that facilitates the unidirectional flow of current generated by sunlight absorption.

Power and Voltage Characteristics of a Typical Solar Cell

A typical solar cell exhibits a characteristic current-voltage (I-V) curve. Under illumination, it produces a short-circuit current (Isc) at zero voltage and a maximum power point (Vmp and Imp), where the product of voltage and current is highest. As the load increases, the current decreases, and the voltage nears the open-circuit voltage (Voc). The maximum power point signifies the optimal load for energy extraction. The efficiency of the cell depends on this maximum power relative to the incident solar power. Typically, commercial solar cells have efficiencies around 15-20%, with designs continually improving these metrics. The shape of the I-V curve is crucial for understanding the performance and potential of solar energy systems.

References

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