photovoltaic cell or photoelectric cell


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The solar cell works in three steps:

1. Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon.
2. Electrons (negatively charged) are knocked loose from their atoms, causing an electric potential difference. Current starts flowing through the material to cancel the potential and this electricity is captured. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.
3. An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity.



Theory:-


A solar cell (also called photovoltaic cell or photoelectric cell) is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect.
Assemblies of solar cells are used to make solar modules which are used to capture energy from sunlight. When multiple modules are assembled together (such as prior to installation on a pole-mounted tracker system), the resulting integrated group of modules all oriented in one plane is referred to in the solar industry as a solar panel. The electrical energy generated from solar modules, referred to as solar power, is an example of solar energy.
Photovoltaics is the field of technology and research related to the practical application of photovoltaic cells in producing electricity from light, though it is often used specifically to refer to the generation of electricity from sunlight.
Cells are described as photovoltaic cells when the light source is not necessarily sunlight (lamplight,artificial light etc). These are used for detecting light or other electromagnetic radiation near the visible range, for example infrared detectors, or measurement of light intensity.


How does solar energy work ?

Solar energy refers to the sun’s light that has been transformed to electrical power and is a very clean form of energy that doesn’t pollute the environment as most other sources of energy do. Solar energy is categorized into direct or indirect as well as passive or active. It can also be classified according to the mode of harnessing it and these are; solar PV, solar thermal and heat exchange.

Factors determining how solar energy works
There are a number of factors that determine how solar energy works and also the amount of electricity that is generated by a solar panel including:
• The size of the solar panel and the amount of surface exposed to the sun.
• The strength of the sun- depends on the weather conditions such as rain or clouds.
• Amount of electricity that is required.
• The location of your household or business.
• Pollution or impediments from the sun’s rays.
• The amount of time the solar is exposed to the sun.
• Air density.
In most situations, you are required to have a storage battery to store up excess power that is generated and this can be used later when it’s needed.
How solar energy works
There are several processes that are involved in the conversion of the sun’s radiation to solar energy and then to electricity that you use in your household or business. These processes make use of solar panels and although one of them focuses on the heat from the sun whereas the other focuses on the light from the sun. An efficient solar panel focuses on both.
The process that focuses on the sun’s heat is called solar thermal and the solar energy works here by harnessing the heat. The systems used to convert this heat make use of mirrors or reflectors to concentrate it to very intense heat in a similar way that a magnifying glass is used to start a fire. The heat is concentrated to a liquid in a container- mostly water- or other liquids that retain heat longer than water. Once these liquids are heated to their boiling points they start producing steam and it is this steam that is used to turn turbines, as a result the turning motion of the turbines is used to generate electricity.
This motion creates electricity in a similar way as setting up a coiled wire and rotating it between two magnets to generate an electric current. The second process that focuses on the suns light is called photovoltaic process and makes use of photovoltaic cells to capture light and convert it to direct current. This is done by exciting of electrons so that as they flow a form of current is generated. The principal components of a photovoltaic cell are semiconductors made of silicon crystals that have been doped with other elements such as Phosphorus or Boron. The bottom layer is doped with Boron and is termed as the p-type semiconductor while the upper layer is doped with Phosphorus and is termed as the n-type conductor and the space between them is called the P-N junction. Once the suns light enters the PV cells, its energy is transferred to electrons that are then knocked loose in both semiconductors and they are attracted to the p-type semiconductor however, the electric field at the junction makes this difficult. When you connect to an external circuit you create a path for the flow of electrons which is actually the current necessary for electricity.


p-Types, n-Types, and the Electric Field

To induce the electric field within a PV cell, two separate semiconductors are sandwiched together. The "p" and "n" types of semiconductors correspond to "positive" and "negative" because of their abundance of holes or electrons (the extra electrons make an "n" type because an electron actually has a negative charge).
Although both materials are electrically neutral, n-type silicon has excess electrons and p-type silicon has excess holes. Sandwiching these together creates a p/n junction at their interface, thereby creating an electric field.
When the p-type and n-type semiconductors are sandwiched together, the excess electrons in the n-type material flow to the p-type, and the holes thereby vacated during this process flow to the n-type. (The concept of a hole moving is somewhat like looking at a bubble in a liquid. Although it's the liquid that is actually moving, it's easier to describe the motion of the bubble as it moves in the opposite direction.) Through this electron and hole flow, the two semiconductors act as a battery, creating an electric field at the surface where they meet (known as the "junction"). It's this field that causes the electrons to jump from the semiconductor out toward the surface and make them available for the electrical circuit. At this same time, the holes move in the opposite direction, toward the positive surface, where they await incoming electrons.

Making n and p Material

The most common way of making p-type or n-type silicon material is to add an element that has an extra electron or is lacking an electron. In silicon, we use a process called "doping."
We'll use silicon as an example because crystalline silicon was the semiconductor material used in the earliest successful PV devices, it's still the most widely used PV material, and, although other PV materials and designs exploit the PV effect in slightly different ways, knowing how the effect works in crystalline silicon gives us a basic understanding of how it works in all devices.