Solar cell Vs. Diode: Key Differences
Both solar cells and diodes are semiconductor devices. When we start knowing about semiconductor devices, at the very first, we get to know about diodes. And solar cells are something that is getting popular with the increasing hype about green energy (and you know how popular solar energy is amongst all other green energy sources).
But if you want to know what solar cells are, I must say it’s nothing but a diode. Wait! I can explain. Solar cells are nothing but a diode, but we need to know what is resisting us from addressing them with a “diode” suffix just like other diodes. Let’s discuss.
What is a Diode?
While introducing diodes, we must know about semiconductors. Semiconductors are something betwixt and between conductors and non-conductors. So, it’s clear that they don’t conduct electricity just as well as conductors do.
But they are so popular and helpful because we can control how well they will conduct by adding impurities into them. The amount of impurities in an intrinsic semiconductor (Silicon, Germanium, etc.) defines how well it will conduct.
We can typically add two kinds of impurities to them; positive and negative. Semiconductors with positive impurities are called p-type semiconductors, and that with negative impurities are called n-type semiconductors. When we combine p-type and n-type semiconductors, that device is called a diode.
The junction of the two types of semiconductors shows some special properties. That is where charge carriers are created when the device is connected to a power supply.
The n-side is connected to the negative electrode (cathode), and the p-side is connected to the positive electrode (anode). This is called forward bias. And if we reverse the connection, then it is called reverse bias.
What is a Solar Cell?
From its name, we can guess that it’s the building block/smallest unit (just like cells are) of a solar panel. So yeah, several solar cells together, one big solar panel absorbing sunlight and converting it to electricity.
As I’ve said, solar cells are one kind of diode made of silicon in general. It is often called a “photovoltaic cell,” too. Converting the sun’s illumination into DC electricity is called the “photovoltaic effect .”
Sunlight reaches the junction of solar cells, and the energy of the radiation creates pairs of positive and negative charge carriers. These charge carriers flow in opposite directions to create electricity flow.
What is meant by a “Normal diode”?
There are several different diodes. Most commons are p-n junction diode, Zener diode, photodiode, and Light-emitting diode (LED).
Others are Schottky junction diode, tunnel diode, laser diode, PIN diode, Gunn diode, etc. But when we say the word diode, it means p-n junction diode. It is the most elementary of all the diodes I mentioned above.
Those diodes are different based on their structure and the material they are made of, and they are used for different applications and purposes. A p-n junction diode is not very widely used, but it’s the simplest according to the structure.
Key Differences Between Solar Cell and Normal Diode
Material
We can find different types of solar cells
- Monocrystalline silicon solar cells,
- III-V semiconductor solar cells,
- Amorphous silicon solar cells,
- Perovskite solar cells, organic solar cells,
- Graphene solar cells, etc.
Monocrystalline silicon solar cells are made from large single crystal silicon, and it has a low absorption coefficient but high efficiency.
But silicon alone isn’t an excellent material for manufacturing solar cells. So, it also is made of alloys that contain the same amount (No. of atoms) of group-III and group-V elements (groups from the periodic table).
Group-III elements include boron, aluminum, gallium, indium, etc.
Group-V elements include phosphorus, arsenic, antimony, bismuth, etc. The atoms are arranged in a ‘zincblende crystal structure’ in an III-V semiconductor. Amorphous silicon solar cells are the best product of thin-film technology.
This isn’t a perfect crystal-like monocrystalline one, and this crystal mismatch increases the ability to absorb light. Some modern solar cells are copper-indium gallium diselenide, cadmium telluride, and even graphene.
On the other hand, p-n junction diodes are simply made of semiconductors with added impurities. N-type semiconductors contain group-V elements, whereas p-type ones contain group-III elements.
But in this case, the proportion of semiconductor and impurities are very large. The extrinsic semiconductor may contain one impurity atom per 108-109 atoms, and highly doped ones may contain 1impurity atom per 105-106 atoms.
Structural Difference
Solar cells have several layers: a base that is made of a p-type semiconductor, a thin and transparent layer of n-type semiconductor, and an anti-reflection coating.
A depletion region is created at the p and n layers junction, and we need sunlight to fall upon the depletion region to create an electric current. Also, some finger-like structures are made at the surface of the n layer to increase the surface area.
P-n junction diode is made simply by joining two types of semiconductors, and it’s a two-terminal device (solar cells too). The layers on both sides can have the same or different thicknesses depending on the usage, and the amount of doping can also differ on both sides.
Working Principle
When it comes to the working principles of semiconductor devices, we should focus on the I-V characteristics of the devices.
In the case of solar cells, the I-V characteristics graph lies in the fourth quadrant (positive voltage and negative current).
A negative current implies that it doesn’t draw current from any power supply; instead, it supplies current to the load. It always works in forwarding bias.
In the case of the p-n junction diode, the I-V characteristics lie in the first quadrant (forward bias). The reverse bias characteristics lie in the third quadrant, but a standard p-n junction diode can’t sustain reverse bias.
It reaches the breakdown condition soon and is damaged beyond repair. So, the p-n junction diode generally is used in forwarding bias.
Applications
There are so many applications of solar cells, and the major usage is solar panels that supply electricity in households.
Many electronic gadgets run on solar cells. Toys, watch, calculators, and many more portable devices are being powered up by solar cells. In the case of electric fencing and remote lighting systems, solar cells are also widely used.
They are used in satellites and spaceships too. In many fields, they are used as emergency power supplies. Solar heaters, solar cookers, and solar devices run solely upon solar cells.
A typical diode doesn’t allow current flow when connected in reverse bias. Due to these characteristics, it is often used for rectification, i.e., conversion from AC to DC. They can also shape waves in clipping circuits. They are used in clamping circuits for DC restoration, voltage multipliers, digital logic circuits as a switch, and voltage regulators.
Conclusion
So, in conclusion, despite being a diode itself, solar cells are much different from “normal” diodes, and they differ in materials, structure, working principle, and applications.
While ordinary diodes are the most elementary semiconductor device, solar cells are a gift of advanced technology, and it’s becoming more and more advanced with proceeding technology. But still, ordinary diodes are the base of many semiconductor devices.
