Panels photovoltaic solar energy

What is the difference between a photodiode and a solar cell?

What is the difference between a photodiode and a solar cell?

Solar cells and photodiodes are different devices that can convert light energy into electricity. Semiconductor devices are important in electronic devices because of their unique characteristics.

Photodiodes and solar cells are diodes, but their purposes and functions differ.

On the one hand, solar cells are PN junction semiconductor devices without any voltage applied across the junction. Moreover, they absorb light and convert it into electrical energy without any chemical reaction.

On the other hand, photodiodes are PN junction diodes with the reverse biased condition. Therefore, the diode is in reversed bias condition when the negative diode’s side is connected to the negative terminal, and the positive side is connected to the battery’s positive terminal. As a result, photodiodes can detect light quickly. 

What is a solar cell?

In electronics, a photovoltaic cell - or solar cell - is an electrical device that converts incident energy from solar radiation into electricity through the photovoltaic effect. Therefore, solar cells are the basis of solar power to transform solar energy into electrical energy.

Compounds of a material that has a photoelectric effect absorb photons from light when hit on the cell's surface and emit electrons. When these free electrons are captured, the result is an electrical current that can be used as electricity.

Photovoltaic panels are made up of several groups of solar cells connected. Each group of photovoltaic cells forms a network of photovoltaic cells connected in series to an electrical circuit to increase the output voltage. At the same time, several networks are also connected in parallel to increase the intensity of the electrical current that the device is capable of providing.

The type of electrical current that solar photovoltaic panels provide is direct current.

What is a photodiode?

A photodiode is a semiconductor device that converts light into an electrical current. It is made up of two regions: the p-type and n-type regions. When light hits the photodiode, it creates an electric field that forces electrons from the n-type region to the p-type region. It creates a current that can be measured.

It is sensitive to the incidence of visible or infrared light. For its operation to be correct, it is polarized inversely, producing a specific flow of current when it is excited by light. Due to their construction, photodiodes behave like photovoltaic cells. When illuminated without an external energy source, they generate a tiny current with the positive at the anode and the negative at the cathode.

Photodiodes absorb light, and the photons inside them get the energy to escape. This results in generating electric current. Photodiodes are a type of light sensor.

What is the difference between a photodiode and a solar cell?

A solar cell is a photovoltaic cell that converts light into electricity. A photodiode is a semiconductor device that converts light into an electrical current.

The most significant major differences between solar cells and photodiodes are:

  • The material used: Most solar cells are made of semiconductor materials like silicon. Photodiodes are typically composed of silicon and gallium arsenide (GaAs). However, they can also be made of other materials such as germanium, indium, lead sulfide, etc.

  • The electronic construction: PV cells are arranged in arrays. Solar cells are electrically connected, forming a solar panel. In contrast, a photodiode consists of a p-n junction made of light-sensitive semiconductor materials. When light shines on the photodiode, it creates an electrical current.

  • The function: solar power systems use photovoltaic cells to absorb sunlight and generate electricity. Meanwhile, photodiodes are sensors or light detectors best used for visible light spectrum, UV, and infrared spectrum.

  • The amount of energy created: a photodiode only converts a small amount of light into electricity, while a PV solar cell can convert much more sunlight into electrical energy. For this reason, solar cells are much larger than photodiodes. In solar cells, we want to absorb as much sunlight as possible. Therefore, we want absorption efficiency over response time.

Structure of a photovoltaic (PV) cell

The most common solar cells are formed by a layer of crystalline silicon with a thickness of approximately 0.3 mm. The manufacturing process is of a sophisticated and delicate level to achieve homogeneity of the material.

Silicon is currently the most widely used material in creating new photovoltaic cells. This material, the most abundant chemical compound in the Earth's crust, is obtained by reducing silica. The first step is to create metallurgical silicon, 98% pure, from quartz stones derived from a mineral vein (the creation technique has nothing to do with sand).

Photovoltaic grade silicon must be transparent to 99.999%. In addition, the silicon must be distilled into a particular chemical compound to obtain this purity.

The positive and negative zones of the solar cell

The electric field is generated from the different polarization of two zones of the photovoltaic cell. Generally, the top part is negatively charged, and the rest are positively charged to create the PN junction.

The P zone (positive zone or receptor anode) is a zone that lacks electrons and therefore has a positive charge. Generally, this configuration is achieved by adding a small part of the boron with only three valence electrons to pure silicon.

The N zone (negative zone, cathode, or emitter) has excess electrons. Generally, this area is formed by the diffusion of phosphor with 5 electrons in the last orbit.

Due to this difference in electric charge in the type of semiconductors, the electric field in the task of pushing the electrons from the N layer to the P layer is produced.

The average conversion efficiency obtained by available PV solar cells produced from silicon is lower than that of multilayer cells, typically gallium arsenide.

Currently, there are also new technologies in producing solar panels that do not use silicon cells.

How does a photovoltaic cell work?

Suppose we connect a photovoltaic solar cell to an electrical circuit with resistance (consumption), and at the same time, it receives solar radiation. In that case, a difference in electrical potential will occur between its contacts. This voltage will cause the electrons to circulate through the charge.

Under these conditions, the PV cell functions as a current generator.

Light is made up of photons that have a certain energy. When the light hits the solar cell, the photons hit the electrons in the N shell. If an electron absorbs the power of a photon with sufficient energy, the electron is ripped from the material leaving a free space that another electron will occupy. This movement of electrons involves an electric current.

The current generated by an illuminated photovoltaic solar cell connected to a load is the remainder between its gross production capacity and the losses due to recombination between electrons and photons.

Uses of photovoltaic solar cells

Photovoltaic cells are sometimes used alone (garden lighting, calculators, ...) or grouped in photovoltaic solar panels. In this way electricity is generated through this renewable energy source.

Photovoltaic cells are the basic components of photovoltaic modules, which are solar panels capable of generating electrical energy from solar radiation. It is, therefore, the essential building block for this type of renewable energy.

A photovoltaic solar panel consists of an array of solar cells connected in series circuit to increase the output voltage. At the same time, several networks are connected in parallel circuits to increase the electrical current that the device is capable of providing.

The type of electrical current that a photovoltaic panel provides is direct current.

Photoelectric cells are also used to replace batteries in applications such as calculators, watches, gadgets, which can run on solar energy.

It is possible to increase its range of use by storing energy by means of a capacitor or a galvanic cell (battery). When used with an energy storage device, a diode must be placed in series to prevent discharge from the system overnight.

Publication Date: February 18, 2016
Last Revision: November 9, 2022