Solar Cell uses Solar Energy which is sustainable and eco-friendly method of producing energy. This post will discuss in detail what is a Solar Cell, types, how it works, Perovskite Solar Cell Revolution, its applications, advantages and disadvantages.
What is Solar Cell
Solar Cell converts light (optical) energy to current. It is basically a Photovoltaic cell which produces voltage when exposed to light. Solar Cells absorb sunlight efficiently and acts as a battery when it is exposed to light energy. Group of Solar Cells is called as Solar module/ Panel and group of Panels assembled together is called as Solar Array.
Fig. 1 – Introduction to Solar Cell
Daryl Chapin along with his colleagues at Bell Labs, invented the first practical device for converting sunlight to electrical energy. In the year 1954, the first Silicon Solar Cell was introduced to the world by Bell Labs. They are used in many devices like calculators, roof top solar panels for domestic use etc.
Photovoltaic cell or Solar Cell has two layers i.e., positive layer (p-type) and negative layer (n-type). Traditionally the Cells were made of Silicon single crystal and it is still the popular choice of today. As we are aware that Silicon is a poor conductor of electricity, doping of Silicon becomes necessary. To create n-type and p-type regions, Silicon is doped with phosphorus and Boron respectively. The p-n junction thus produces Electric field and acts as a Diode which helps in the movement of Electrons from p-region to n-region.
Fig. 2 – Solar Cell, Panel, Array
Types of Solar Cells
They are classified into three types. They are:
- First Generation Cells
- Second Generation Cells
- Third Generation Cells
First Generation Cells
This generation of Solar Cells comprises of single crystal and multi-crystalline Silicon Cells. These are the oldest and were introduced by Bell Labs. These cells are known for its efficiency. These Cells are produced on Silicon Wafer and each cell can supply 2-3 Watts power. Solar Cells are combined to form Solar Modules/ Panels to increase the power. These cells are expensive to produce.
Fig. 3 – Daryl Chapin – Inventor of Solar Cell
Second Generation Cells
Second Generation Cells are known for its Thin Film Cells that includes Amorphous Silicon based Thin- Film solar cells, Cadmium Telluride/Cadmium Sulphide solar cells and Copper Indium Gallium Selenide (CIGS) solar cells. Their efficiency is lower than the first-generation cells and are cost-effective to produce. These cells are made of successive layers which are 1-4 μm thick and are deposited on various types of substrates such as glass, polymer or metal. They are visually appealing and flexible. Amorphous Silicon cells are used in Calculators.
Fig. 4 – Thin Film Cells (Second Generation Cells)
Third Generation Cells
Third Generation Cells includes latest and upcoming technologies which look promising. The main objective of the research is to produce most effective Solar Cells which are inexpensive to produce. They are also aiming at toxic-free cells. Third generation cells include Nanocrystal based solar cells, Polymer based solar cells, Dye Sensitized cells and Organic–inorganic Halide Perovskite cells.
Perovskite Solar Revolution
Perovskite Solar Cell Technology has seen a rapid improvement in the recent years. Perovskite is a type of mineral having properties like super conductivity and magneto resistance and hence is the ideal choice of future Solar Cells. They are also called third-generation cells. Perovskite Cells are very efficient and exhibit extremely high light absorption attributes. Perovskite-Silicon Cells which was developed recently is non-toxic and manufactured from materials which are abundantly found on Earth.
Fig. 5 – Third Generation Cells (Perovskite Solar Cells)
How does Solar Cell Work
To understand the working principle, let us consider Solar Cell made of Silicon and has positive layer (p-type) and negative layer (n-type). To create p-type region, Silicon is doped with Boron which has one less electron in their Valence Shell as compared to Silicon. Thus, Electron Valency or ‘hole’ is created. Similarly, n-type region is formed by doping with Phosphorus which has one more electron in their Valence Shell as compared to Silicon. When Covalent bonding occurs, one Electron is free to move.
Solar Cell is a sandwich of n-type and p-type Silicon layer. When the Solar Cell is exposed to Sunlight, the Electrons and holes are close to each other at the junction of two layers. By Coulombs law, there is a force between Electrons and holes which makes the Electrons from n-region move to p-region and occupies holes. This results in negative ions on p-side and positive ions on n-side.
Fig. 6 – Working Principle of Solar Cell
Thus, Depletion layer is formed and prevents further flow of electrons. Electric field is generated due to the presence of oppositely charged ions. When the n-type and p-type layers are connected externally to a metallic wire, then electrons move from n-region to p-region crossing the depletion layer and travels through the metallic wire to n-region. This creates flow of electricity.
Applications of Solar Cell
The applications include:
- They are used in portable power supplies.
- They are widely used for water pumping, heating etc.
- They are used in Solar Power Satellites.
- They are used in watches and calculators.
- They are used in street lighting systems.
Advantages of Solar Cell
The advantages include:
- It is sustainable and renewable form of energy.
- Maintenance is low.
- Durability is high.
- Raw materials required to produce Third-generation Cells are inexpensive.
Disadvantages of Solar Cell
The disadvantages are:
- Initial installation of Solar panel is expensive.
- Dependency on Weather conditions affects its efficiency.
- Damaged Solar panel system may lead to Electric shorts and house fires.
- Occupies lot of space.
- They are more susceptible to damage.
- Second-generation Cells, made of Cadmium are highly toxic.
- Raw materials required to produce Second-generation Cells are expensive.
The research and development of Solar Cells continues to harness the abundant energy of ‘Sun’ which will reduce the use of fossil fuels.