What is a Solar Cell? Understanding its Functioning, Types, and Manufacturing Process
A solar cell is the engine of a solar panel. Solar electricity is generated when the solar cells convert sunlight into electricity. While solar cells are most commonly made of silicon, they can also be made of materials such as organic materials.
To understand what is a solar cell, you need to understand how they are made, how they function, and the different types of solar cells currently available and under development.
A solar cell is a device which converts sunlight into electricity. It is also called a photovoltaic (PV) cell because it uses the photovoltaic effect to generate electricity.
Solar cells are the most basic components of a solar panel. They are usually made of silicon but can also be made of organic and other materials.
How Solar Cells are Made
Here is a brief description of the steps required to manufacture a solar cell:
- Purification of Silicon to Produce Pure Silicon: Impure silicon is heated with carbon to produce 99% pure silicon. Thereafter, methods such as the floating zone technique are used to produce 100% pure silicon.
- Ingot Creation: The silicon is heated and molten into a rectangular shape called an ingot.
- Wafer Creation: Diamond-coated wire saws are used to slice the ingots into wafers.
- Cell Fabrication: Sawdust is removed from the solar cells and anti-reflective courting is added to it.
- Soldering Fingers and Busbars: Fingers and busbars are soldered to the solar cells so that electricity can flow through them.
To learn about the solar cell manufacturing process in detail, you can read our blog on how solar panels are made.
How a Solar Cell Functions
There are 2 main aspects of how a solar cell functions. One is the internal electric field created by the p-n junction and the other is the flow of electricity through the external circuit.
We will explore these aspects one by one:
- The Role of Internal Electric Field
The solar cell consists of 2 sides: p-side and n-side. The p-side is doped with boron and the n-side is doped with phosphorus.
Please take note of the fact that silicon has 4 electrons in its outer shell, boron has 3 electrons in its outer shell, and phosphorus has 5 electrons in its outer shell. The gravity of this fact will be clear in the following paragraphs.
The p-side has a deficit of electrons. This is due to boron having 1 electron less than silicon in its outer shell. It leads to boron having 1 electron less for forming bonds with silicon, thus leaving a “hole”.
The n-side has a surplus of electrons. This is due to the phosphorus’s outer shell having 1 electron more than that of silicon. It leads to phosphorus having 1 electron more than silicon after forming bonds with its 4 outer electrons. The surplus electron leads to an overall negative charge.
The p-side and n-side are placed side-by-side. At the junction of these 2 layers, a depletion zone is created. Let’s understand what it is.
The electrons from the n-side move towards the holes on the p-side. Thus, the holes in the p-side get filled with the electrons from the n-side, leaving behind holes on the n-side.
The rearrangement of holes and electrons in the depletion zone leads to an electric field within it. Its importance will be clear in the next section.
- How Sunlight is Converted to Electricity
The n-side of the solar cell faces the sun. When sunlight falls on the solar panels, it excites the electrons in the silicon atoms by imparting energy to them. The electrons are displaced and attracted to the holes on the p-side, but they cannot go through the depletion zone because they are repelled by their electric field.
When the solar panels are connected to an external circuit, the electrons flow through it, thus leading to the generation of electricity.
Role of Silicon in Solar Cells
Here are some of the reasons why silicon is used to create silicon cells:
- Silicon is the 2nd most abundant element on earth. Thus, it is easily available and cost-effective as a raw material.
- It has a bandgap of 1.1 eV, which is close to the desired bandgap of 1.34 eV which is needed for generating solar electricity.
- In TOPCon solar cells, the efficiency can go over 20%.
- Solar panels with silicon solar cells can last over 25 years while producing about 80% of their initial capacity even in the 30th year.
- Unlike certain other materials which can be used to make solar cells, silicon is not toxic.
Types of Solar Cells
Here are the types of solar cells which are used or can be used in solar panels in the future:
- Monocrystalline Solar Cell: It comprises solar cells which are made from a single crystal of silicon.
- Polycrystalline Solar Cell: Multiple silicon crystals are used to make polycrystalline solar cells.
- Thin-Film Solar Cell: 4 materials are commonly used to make thin-film solar cells: Cadmium Telluride (CdTe), Amorphous Silicon (a-Si), Copper Indium Gallium Selenide (CIGS), and Gallium Arsenide (GaAs). They have lower efficiency than crystalline solar cells.
- Perovskite Solar Cell: These solar cells are currently in the development phase. In the lab, they have reached efficiencies of 20%, and it could increase in the future.
- Multijunction Solar Cell: These solar cells can have an efficiency of over 45%. Currently, they are not commercially available.
- Organic Solar Cell: Their flexibility makes them suitable for a variety of applications but their efficiency is lower than that of traditional solar panels.
The technology used in a solar cell distinguishes it. While the answer to what is a solar cell is fixed, its application can vary depending on circumstances and the technology which has been used in it.
The selection of solar cell type must be guided by factors such as efficiency, cost, requirements, and space availability. Crystalline silicon remains the most popular choice due to its balance of efficiency and cost-effectiveness, while thin-film technologies offer flexibility and lightweight options.
Frequently Asked Questions
A solar cell generates electricity by converting sunlight into electricity. It is an integral component of a solar panel.
Solar cells made of silicon are most commonly used in solar panels.
Sunlight is converted into electricity via the photovoltaic effect.
Solar electricity generation will take place if sunlight falls on the solar panels. Even in rainy weather, if sunlight falls on the solar panels, the solar cells will generate electricity.
