monocrystalline silicon photovoltaic cell

Common types of silicon solar cells for photovoltaic modules

There are many types of silicon solar cells developed by countries all over the world; the main series are monocrystalline and polycrystalline.

Solar cells, also called photovoltaic cells, are devices that can generate electricity under sunlight. In 1921, Albert Einstein won the Nobel Prize in Physics for his discovery of the photoelectric effect, which is the scientific principle of solar cells. Solar cells were first used in space exploration in the 1950s. Solar cells are ideal for this type of application because of their high reliability, no maintenance (no moving parts), and only sunlight. For this type of application, sunlight is almost unlimited energy. In the 21st century, considering the problems caused by greenhouse gas emissions and insufficient fossil fuel reserves, solar cells have become an increasingly attractive energy source. The popularity of solar cells is also due to their diversity, which can be used on a small scale (such as home use or to supply power to a single device in a remote telecommunication relay station), and can also be used for large-scale power supply.

The potential of photovoltaic power generation has attracted a lot of government and commercial investment from all over the world. Around the world, many laboratories are committed to improving the efficiency of solar cells, by upgrading existing technologies, using new materials, and new manufacturing methods to develop more powerful batteries.

Semiconductor device

Solar cells are made of semiconductor materials. Semiconductor materials conduct electricity under certain conditions, so they are neither insulators nor conductors. The most common semiconductor material is silicon. In order to improve conductivity, it is generally combined with other elements through a “doping” process. Semiconductors are often used in electronic devices, including photovoltaic cells, light-emitting diodes (LEDs), and microchips (such as those used in computers).

 Mainstream technology

Silicon is the most widely used material in solar cell manufacturing, and most commercial solar cells are made of silicon. Silicon is extracted from silicon dioxide (also called quartz), which can be mined and refined to make solar cells. Quartz crystal is also the main component of sand, but ordinary sand has too many impurities to be used.

Silicon is a diverse material: a non-metallic material that not only exhibits many characteristics of metal (that is, it is shiny and solid at room temperature), but also exhibits some characteristics of non-metal. There are several different types of silicon solar cells: monocrystalline silicon, polycrystalline silicon, and amorphous silicon cells.

Semiconductor materials are used in many electronic components.

Monocrystalline silicon battery

To manufacture this type of battery, a silicon seed crystal is placed in a crucible containing molten silicon, and it is slowly pulled out while rotating. In this way, a larger pure crystalline silicon ingot can be made, which can then be cut into thin silicon wafers. Monocrystalline silicon solar cells have the highest efficiency and are generally the most expensive. Compared with other silicon cell technologies, due to their higher efficiency, they can be

In order to increase the output power, it is reasonable that the initial cost is higher. The highest efficiency record of monocrystalline silicon solar cells is 25%. The current commercial solar cell efficiency is 22.5%, and the final module efficiency is 19%.

Monocrystalline silicon ingot
Monocrystalline silicon ingot

Polycrystalline silicon battery

The manufacture of polycrystalline silicon cells is carried out by silicon ingots, so they are not single crystal silicon ingots, but silicon ingots composed of many small crystals. These small crystals grow in any direction during the solidification of the molten material. This makes the efficiency lower than that of monocrystalline silicon cells, but because it is simpler and cheaper, this is still a very common technology. Polycrystalline silicon cells and monocrystalline silicon cells are the two most commonly used types in photovoltaic arrays. The laboratory efficiency of current commercial polycrystalline silicon solar cells is higher than 18%, and the most isotropic average record of modules is 17.84%.

monocrystalline silicon photovoltaic cell
a monocrystalline silicon photovoltaic cell with an efficiency of 22% is used on the Sunswift IV. This is the silicon solar car that won the World Solar Challenge held in Australia in 2009. This battery can also for photovoltaic roofs and grid-connected photovoltaic systems
Polysilicon cells are easy to distinguish because of their unique texture structure
Polysilicon cells are easy to distinguish because of their unique texture structure

Thin film solar cell

Thin-film solar cells are made of materials suitable for large-area deposition, and may be only about 1um thick, so they are called thin films (a dot “.ยท” covers 615um). The thickness of polycrystalline silicon and monocrystalline silicon solar cells is generally 300 um).

The rise in material prices and the high demand for photovoltaics worldwide have aroused people’s interest in thin-film solar cells. The manufacture of thin-film solar cells is cheaper than crystalline silicon solar cells. A lot of research has been carried out to improve the efficiency. The current laboratory record of the efficiency of thin-film solar cells is 20.1%. However, the efficiency of commercial thin-film battery modules is between 6% and 12%. Thin-film solar cells are used more and more frequently in buildings, and are usually used in some solar-powered watches, calculators and other gadgets.

The most common thin film materials are amorphous silicon (a-Si, another form of silicon), cadmium telluride (cdTe), and copper (gallium) selenium (CIS or CIGS). Inside the amorphous silicon material, molecules are randomly doped together instead of forming a crystal structure like monocrystalline silicon and polycrystalline silicon. CdTe, CIS and CIGS are all polycrystalline materials, and their internal structure is similar to polycrystalline silicon materials, but their materials are very different. Thin-film solar cells are suitable for large-scale production and can be prepared by chemical vapor deposition (CVD). The thin-film materials are deposited on large-area materials such as coated glass, flexible plastic or stainless steel.

Battery materialModule efficiency (%)1kWp module area/m31kWp module Guoji/ft2
Monocrystalline silicon14~205~754~77
Amorphous silicon film6~911~16.5110~179
CdTe film9~119~1198~110
CIS/CIGS film10~128.5~1090~108
Table 3-1 Comparison of different solar cell technologies

The size of the array largely depends on the efficiency of the components, although the most efficient components may not be the most suitable. Modules with lower efficiency are usually cheaper, and where the space of the photovoltaic array is not constrained, the cost-effectiveness may also be the best.

Amorphous silicon components
Amorphous silicon components are easily distinguished from crystalline silicon components by their uniform dark color, but they look a lot like non-silicon thin film components