Basics of Solar Photovoltaic Cells

A solar cell or photovoltaic (PV) cell can pass through, absorb, or reflect light that strikes it. More efficiently than an insulator, the semiconductor material that makes up a PV cell can conduct electricity, but not as well as a good conductor like a metal. A variety of semiconductor materials are used in PV cells.

Light energy is absorbed by and transferred to the negatively charged electrons in a semiconductor when it is exposed to light. The extra energy gives the electrons the ability to move an electrical current through the substance.

A PV cell’s efficiency can be calculated as the ratio of the electrical power it produces to the energy from the light shining on it.The cell’s ability to transform energy from one form to another is demonstrated by this ratio.The qualities of the available light (such as its intensity and wavelengths) and a number of cell performance factors determine how much power is generated by PV cells.

The bandgap, which describes what wavelengths of light the substance can absorb and convert to electrical energy, is a crucial characteristic of PV semiconductors. The PV cell can effectively use all of the available energy if the semiconductor’s bandgap matches the wavelengths of light shining on it.

More information on the most popular semiconductor materials for PV cells is provided below.

SILICON

With silicon accounting for over 95% of the modules supplied today, silicon is by far the most prevalent semiconductor material used in solar cells. In addition, it is the most widely utilized semiconductor in computer chips and the second most abundant element on Earth (after oxygen). Cells made of crystalline silicon are composed of silicon atoms that are linked together to form a crystal lattice. The efficiency of converting light into electricity is increased by the well-organized structure provided by this lattice.

Currently, silicon-based solar cells offer a mix of high efficiency, low cost, and long lifespan. Modules should last for at least 25 years and continue to generate more than 80% of their initial power after that.

THIN-FILM PHOTOVOLTAICS

One or more thin layers of PV material are deposited on a support material, such as glass, plastic, or metal, to create a thin-film solar cell. Cadmium telluride (CdTe) and copper indium gallium diselenide are the two primary types of thin-film PV semiconductors available today (CIGS). The surface of the module can be directly coated with either substance.

After silicon, CdTe is the second most used PV material, and CdTe cells may be produced utilizing low-cost production techniques. Even though they are now a more affordable option, silicon still has higher efficiency levels. Although CIGS cells exhibit great efficiencies and ideal PV material qualities in the lab, the intricacy of combining four parts makes the move from the lab to production more difficult. Both CdTe and CIGS require greater shielding than silicon for prolonged outdoor operation.

PEROVSKITE PHOTOVOLTAICS

Thin-film cells known as perovskite solar cells get their name from their distinctive crystal structure. Perovskite cells are made up of layers of materials that are printed, coated, or vacuum-deposited onto a supporting layer underneath known as the substrate. They can achieve efficiency comparable to crystalline silicon and are often simple to construct. Perovskite solar cells’ efficiency in the lab have increased more quickly than those of any other PV material, going from 3% in 2009 to over 25% in 2020. Perovskite PV cells need to be stable enough to endure 20 years outside in order to be commercially viable, thus researchers are working on improving their durability and creating high-volume, low-cost manufacturing processes.

OPEN SOURCE PHOTOVOLTAICS

Organic PV, or OPV, cells are made of organic compounds rich in carbon and can be designed to improve a particular PV cell property, such as bandgap, transparency, or color. Although OPV cells are currently only about half as efficient and have shorter working lives as crystalline silicon cells, they may be less expensive to produce in large quantities. They can also be used with a variety of supporting materials, like flexible plastic, expanding the uses of OPV. PV

QUANTUM DOTS

Quantum dots, which are nanometer-sized semiconductor materials, are used in quantum dot solar cells to conduct electricity. Although quantum dots offer a novel method for processing semiconductor materials, they are currently not very effective due to the difficulty of establishing an electrical connection between them. They can, however, be easily converted into solar cells. A spin-coat technique, a spray, or roll-to-roll printers like those used to print newspapers can all be used to deposit them onto a substrate.

Quantum dots can be combined with other semiconductors, such as perovskites, to improve the performance of a multijunction solar cell since they are available in a range of sizes and have a flexible bandgap. This allows them to catch light that is challenging to capture (more on those below).

PHOTOVOLTAICS MULTIJUNCTION

Multijunction solar cells are created by overlaying various semiconductors to increase PV cell efficiency. Unlike single-junction cells, which contain just one semiconductor, these cells are effectively stacks of various semiconductor materials. Since each layer’s bandgap varies, they each absorb a unique portion of the solar spectrum, utilizing more of the sun’s energy than single-junction cells. Because a layer below the first semiconductor layer absorbs the light that isn’t absorbed by it, multijunction solar cells can achieve record levels of efficiency.

A solar cell having precisely two bandgaps is referred to as a tandem solar cell, whereas all solar cells with more than one bandgap are multijunction solar cells. Multijunction III-V solar cells are multijunction solar cells that incorporate semiconductors from columns III and V of the periodic table.

Multijunction solar cells have shown efficiency greater than 45%, but because they are expensive and challenging to produce, they are only used in space exploration. III-V solar cells are used by the military in drones, and scientists are looking into other applications where high efficiency is important.

CONCENTRATION PHOTOVOLTAICS

By using a mirror or lens, concentration PV, sometimes referred to as CPV, concentrates sunlight onto a solar cell. Since sunlight is focussed into a smaller area, less PV material is required. The highest overall efficiencies are attained using CPV cells and modules because PV materials become more effective when light is focused. However, proving the essential cost advantage over today’s high-volume silicon modules has become difficult since it requires more expensive materials, manufacturing procedures, and the capacity to follow the movement of the sun.