What is a photovoltaic cell? Learn about solar energy

When reading about solar energy, you will see the term photovoltaic cell come up regularly. This makes sense as this cell is essential for the production of solar power. If you want to know what this cell is, then you came to the right place. Let’s have a look.

Photovoltaic cells: The technology behind solar energy

Solar energy isn’t a new technology. In fact, it has been around a lot longer than you might think. The first time someone discovered we could harness energy directly from sunlight was in 1839. In Paris, a young physicist named Edmond Becquerel discovered what he called the Becquerel effect. The 19 year old scientist used his father’s laboratory to do experiments on acidic solutions. One day he decided to place silver chloride into one of his solutions and he discovered that, when light shone on to it, it created a current. He named this creation of voltage after himself, so this was the Becquerel effect.

The name changed later on and it became known as the photovoltaic effect. What Becquerel had created was the world’s first photovoltaic cell. Becquerel went on to be a successful physicist and to this day there is an annual Becquerel Prize for outstanding merit in photovoltaics.

What does a photovoltaic cell do?

It would take a while after the discovery before photovoltaic cells became commercially adapted. Only in 1941 did a man called Russell Ohl patent the very first modern solar cell. Today’s solar panels still use photovoltaic cells and are therefore often referred to as PV panels.

When we think about cells, we think about the invisible tiny things that our body is made out of, but a photovoltaic cell is very visible. Its standard size -for solar panels- is 156 millimetres by 156 millimetres, or about 6×6 inches. You can get smaller ones though, these are mainly used for mobile solar panels, or solar phone chargers and such.

A photovoltaic cell needs to do three things. Firstly, it needs to absorb the sunlight that hits its surface. It is worth noting that any type of light would cause the photovoltaic effect. By absorbing the light, photons that are in that light dislodge electrons in the atoms that are in the cell. Second, the photovoltaic cell needs to be receptive for the moving electrons, making them go closer to the front surface. This causes an imbalance in the cell between the front and the back, which creates a voltage. The third necessity is that both the front and the back need to be connected to let the electricity flow to an external circuit.

How does a photovoltaic cell work?

A photovoltaic (PV) cell, commonly referred to as a solar cell, has the ability to either reflect or absorb light. The PV cell is constructed using semiconductor materials, which are superior in their ability to conduct electricity compared to insulators but not as efficient as conductors like metals. Various types of semiconductor materials are utilized in the construction of PV cells.

When light energy is absorbed by the semiconductor material, it is transmitted to the negatively charged particles of the material, also known as electrons. This additional energy allows the electrons to move freely throughout the material, generating an electrical current. Conductive metal contacts in the form of a grid are used to draw electrical current from the solar cells, which can be utilized to power electronics in residential and commercial settings.

The efficiency of PV cells can be evaluated by comparing the amount of electricity produced by the cell to the amount of energy it receives from the incoming light. Several factors influence the amount of energy generated by PV cells, including the light’s characteristics (e.g., intensity and wavelength) and the cell’s own performance attributes.

A crucial characteristic of a PV semiconductor is its bandgap, which determines the range of wavelengths at which the material can absorb light and convert it into electrical energy. The PV cell can utilize the incoming sunlight most effectively if the semiconductor’s bandgap is harmonious with the light’s frequency.

Most commonly-used semiconductor materials for PV cells

In this section we will talk about the five most common semiconductor materials used in solar cells (Source: Solar Energy Technologies Office).

1. Silicon

Approximately 95% of all commercially available modules contain silicon solar cells, making it the most widely used semiconductor material for solar cells. It’s used in most semiconductors and is the second most common material on Earth (after oxygen). The cells of crystalline silicon are constructed from a latticework of interconnected silicon atoms. This lattice provides a well-structured platform for converting light into electricity.

Currently, solar cells made from silicon offer a perfect balance of efficiency, cost, and lifespan. It is predicted that modules will continue to generate over 80% of their initial power output even after 25 years of service.

2. Thin-Film Photovoltaics

To create a thin-film solar cell, PV material is deposited in one or more extremely thin layers onto a substrate (typically glass, plastic, or metal). Thin-film photovoltaic (PV) semiconductors include cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS). Both substances can be deposited straight onto the front or back of the module.

CdTe is the most widely used PV material after silicon because it is inexpensive to produce CdTe cells. Even though they are less expensive than silicon, their efficiency is still lower. In the lab, CIGS cells have high efficiencies and ideal properties for a PV material, but the complexity of combining four elements makes scaling up production difficult. CdTe and CIGS both need more shielding than silicon does to function reliably in the open air for extended periods of time.

3. Perovskite photovoltaics

Perovskite solar cells are a special kind of thin-film cell that gets its name from the crystal structure they use. Layers of materials are printed, coated, or vacuum-deposited onto a substrate to construct a perovskite cell. Typically, they are simple to put together and can achieve efficiencies on par with crystalline silicon. Perovskite solar cells have shown the greatest rate of improvement in laboratory testing, going from 3% efficiency in 2009 to over 25% efficiency in 2020. Researchers are working on making perovskite PV cells more durable and developing large-scale, low-cost manufacturing techniques in order to make them commercially viable in the next 20 years.

4. Organic photovoltaics

Carbon-rich (organic) compounds make up organic photovoltaic (PV) cells, which can be modified to improve the PV cell’s bandgap, transparency, or colour. In comparison to crystalline silicon cells, OPV cells are only about half as efficient right now, and they also have shorter operating lifetimes. However, they may be cheaper to produce in large quantities. OPV’s versatility stems from the fact that it can be applied to many different types of substrates, including plastics that are both rigid and flexible.

5. Quantum dots

Small particles of semiconductor materials measuring a few nanometres in width are used to conduct electricity in quantum dot solar cells. Although quantum dots offer a new way to process semiconductor materials, they are not yet very efficient due to the difficulty of creating an electrical connection between them. To be used as solar cells, however, requires little effort. Spin-coating, spraying, and roll-to-roll printers like those used for printing paper can all be used to deposit them onto a substrate.

So how many photovoltaic cells do I need?

One cell isn’t going to help you much. One conventional solar panel consists of 72 cells. These cells together produce around 250W. For solar energy as renewable energy to be a serious alternative for your own home, you’ll need multiple solar panels on your roof. If you have 10 panels installed, you’ll have 720 cells working for you to create green energy.

Even though we are using technology that is more than 180 years old, there is a lot of development in the production of solar panels. The panels are becoming more and more effective and the cost is dropping significantly. In 1977, the price of 1W of solar energy was $76. In 2015 the same 1W was only $0.30. The more the domestic use of solar panels gains in popularity, the cheaper it will become.

What devices use photovoltaic cells?