Solar cell and Zener diode

Solar Cell

A solar cell (also known as a photovoltaic cell or PV cell) is an electrical device that uses the photovoltaic effect to convert light energy into electrical energy. A solar cell is a p-n junction diode in its most basic form. Solar cells are a type of photoelectric cell, which is defined as a device whose electrical properties such as current, voltage, or resistance, change when exposed to light.

Solar cells can be connected to form modules, which are generally referred to as solar panels. The maximum open-circuit voltage of a standard single junction silicon solar cell is around 0.5 to 0.6 volts. This isn’t much on its own, but keep in mind that these solar cells are tiny. Significant amounts of renewable energy can be generated when solar panels are merged into a huge solar panel.

Construction of Solar Cell

A solar cell is essentially a junction diode, though its construction differs slightly from that of standard p-n junction diodes. On a thicker n-type semiconductor, a very thin layer of p-type semiconductor is developed. On top of the p-type semiconductor layer, we place a few finer electrodes.

The thin p-type layer is not obstructed by these electrodes. A p-n junction exists just under the p-type layer. A current-collecting electrode is also provided at the bottom of the n-type layer. To protect the solar cell from mechanical shock, we encase the complete unit in thin glass.

Working Principle of Solar Cell

When light reaches the p-n junction, photons can readily pass through the thin p-type layer and into the junction. The particles in light energy supply the junction with enough energy to build a number of electron-hole pairs. The incoming light causes the junction’s thermal equilibrium to be broken. The depletion region’s free electrons can swiftly reach the n-type side of the junction.

Similarly, depletion holes can quickly reach the p-type side of the junction. Once the freshly formed free electrons reach the n-type side of the junction, they are unable to cross it due to the junction’s barrier potential.

Similarly, as the freshly generated holes reach the p-type side of the junction, they are no longer able to cross it and have the same barrier potential as the junction. The p-n junction will function like a tiny battery cell when the concentration of electrons increases on one side, i.e., the n-type side of the junction, and the concentration of holes increases on the other side, i.e., the p-type side of the junction. A voltage is established, which is referred to as photovoltage. There will be a little current flowing through the junction if we attach a small load across it.

Zener Diode

A Zener diode is very similar to a PN junction diode. However, it is usually operated in reverse bias mode. This is a heavily doped PN junction diode that has been particularly created. As a result, the Zener diode is a highly doped semiconductor diode that is engineered to work in the opposite direction.

The Zener diode is also a diode that is specifically built for maximising the breakdown region. It signifies that the diode’s n-type material is linked to the power supply’s positive terminal. The P-type material is also linked to the power supply’s negative end. Due to the strongly doped semiconductor material, the depletion region of the diode is extremely thin. 

Zener Diode Specifications

Zener diodes come in a variety of configurations, including nominal working voltage, power dissipation, maximum reverse current, and packaging. The following are some of the most often used Zener Diode specifications:

• Voltage (Vz): The reverse breakdown voltage, which can range from 2.4 V to around 200 V, is referred to as the Zener voltage. Even so, it may reach 1 kV, whereas the surface-mounted device’s maximum voltage is around 47 V.
• Current (Iz -max.): At the rated Zener voltage Vz, the maximum current will range from 200 microamps to 200 amps.
• Current (Iz-min.): The minimal current necessary to break down the diode will be between 5 and 10 mA.
• Power rating: The product of the voltage across the diode and the current flowing through it determines the maximum power that can be dissipated by the Zener diode. 400 mW, 500 mW, 1 W, and 5 W are some common quantities.
• Typically, a voltage tolerance of 5% is used.
• The diode’s temperature stability is around 5 V.
• Surface mount and leaded devices can be used as separate devices or as part of integrated circuits.
• Zener resistance (i.e., Rz): The diode also has a resistance value, which may be seen in the I-V characteristics.

Zener Breakdown

The failure is caused by the Zener breakdown phenomenon, which occurs when the voltage falls below 5.5 volts. It could also have an effect on ionisation that happens at 5.5 Volt. Both processes provide the same results and hence do not necessitate separate circuitry. However, the temperature coefficient for each process is different. The temperature coefficient of the Zener effect is negative, whereas the temperature coefficient of the impact effect is positive. Since the two temperature effects are nearly equivalent, they cancel each other out. Because of this, Zener diodes are the most stable throughout a large temperature range.

Avalanche Breakdown 

At high reverse voltage, avalanche breakdown occurs in both conventional and Zener diodes. When a large amount of reverse voltage is given to the PN junction, the liberated electrons obtain enough energy to accelerate rapidly. These high-velocity free electrons smash with other atoms, knocking off extra electrons. As the electric current in the diode rapidly grows as a result of this continual collision, a significant number of free electrons are created. A typical diode may be permanently destroyed by this abrupt rise in electric current, but a Zener diode is intended to work under avalanche breakdown and can withstand the quick spike of current. In Zener diodes with a Zener voltage (Vz) greater than 6V, avalanche breakdown occurs.

Conclusion

Although solar cells have several drawbacks, these drawbacks are likely to be solved as technology progresses. As technology advances, the cost of solar plates, as well as the cost of installation, will fall, allowing anybody to attempt to install the system. Furthermore, the government is putting a lot of focus on solar energy, so we may predict that in a few years, every residence and every electrical system will be powered by solar or renewable energy.

A Zener diode is a semiconductor device made of silicon that allows current to flow in both directions. When a particular voltage is reached, the diode’s special, highly doped p-n junction is designed to conduct in the other direction.

The Zener diode has a well-defined reverse-breakdown voltage at which it begins to conduct current and may operate in reverse-bias mode indefinitely without damage. Furthermore, the voltage drop across the diode remains constant over a wide range of voltages, making Zener diodes ideal for voltage regulation.