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Crystalline silicon photovoltaics (PV) are the working mother of the photovoltaic industry, invented from the 1950s to the present. Over the past decade, the market share of crystalline silicon photovoltaics has been between 80% and 90%. As one of the most widely used solar cell technologies, crystalline silicon solar cells are currently undergoing a series of technological breakthroughs.
Recently, Longi Green Energy Technology Co., LTD., in a research paper published in the journal Nature, reported for the first time an important achievement of 27% breakthrough in the photoelectric conversion efficiency of crystalline silicon cells. This breakthrough not only marks the crystalline silicon solar cells have entered a new era of high efficiency, but also injected new impetus to the future development of the photovoltaic industry.
Classification of crystalline silicon solar cells
Monocrystalline silicon solar cells Monocrystalline silicon solar cells are made of monocrystalline silicon sheets. In monocrystalline silicon materials, silicon atoms are arranged in an orderly periodic manner in space and have a long-range order. This order is conducive to the improvement of the conversion efficiency of solar cells, the current conversion efficiency of monocrystalline silicon solar cells is 14%-17%, up to 24%.
The production process of monocrystalline silicon solar cells is mature and widely used in aerospace and high-tech products. However, the manufacturing process of monocrystalline silicon solar cells is complicated, and the manufacturing needs large energy consumption and high cost.
Polycrystalline silicon solar cell polycrystalline silicon materials are composed of many single crystal particles (particle diameter of several microns to several millimeters). The size of each single crystal particle, crystal orientation is different from each other, and its conversion efficiency is about 13% to 15%, up to 20%. Polycrystalline silicon solar cells have shorter production time and lower manufacturing cost than monocrystalline silicon solar cells, and have an important position in the market.
Amorphous silicon solar cells Amorphous silicon solar cells are made of very thin amorphous silicon film (about 1 mm thick), silicon material consumption is small, can be directly deposited on a large area of glass plate to generate silicon semiconductor film, the preparation of amorphous silicon process and equipment is simple, short manufacturing time, less energy consumption, suitable for mass production.
The conversion efficiency of amorphous silicon solar cells is 5%-8% and up to 13%, which is characterized by power generation under low light. The main disadvantage of amorphous silicon solar cells is that they are slightly less stable. However, its low price and low light power generation make it widely used in civilian products.
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How crystalline silicon solar cells work
When sunlight hits the surface of a crystalline silicon cell, the silicon material in the cell absorbs light energy. This process allows electrons to gain energy and form free electrons and holes. In the crystalline silicon cell, the absorption of light energy causes electrons to transition from the valence band to the conduction band, forming an electron-hole pair. Electrons are negatively charged, while holes are positively charged.
Crystalline silicon cells are usually composed of two types of P-type and N-type silicon materials, forming a p-n junction. P-type silicon has a large number of holes, while N-type silicon has a large number of free electrons. The electric field at the p-n junction causes electrons and holes to move in opposite directions, with electrons moving towards the N-type region and holes moving towards the P-type region.
When the electrons and holes are separated, the resulting current flows through an external circuit, supplying power to the load. This process is the key to generating electricity in solar cells. The current in the energy storage battery can be sent through the connected wires to an electrical device or storage device, such as a battery pack, for later use.
The efficiency of crystalline silicon solar cells exceeded 27% for the first time
Longi Green Energy Technology Co., LTD. (hereinafter referred to as "Longi"), as the first unit, published an article entitled "Silicon heterojunction back contact solar cells by laser" online in the journal Nature The research paper patterning reported for the first time the research results that the photoelectric conversion efficiency of crystalline silicon cells has broken through 27% through the all-laser patterning process. This breakthrough marks the first time that the efficiency of crystalline silicon solar cells has exceeded 27%, setting a new milestone for photovoltaic technology and industry based on crystalline silicon materials.
The research demonstrates the great potential of backcontact (BC) batteries to achieve high efficiency and low cost. In order to achieve this high conversion efficiency, the Longi Central Research Institute team has carried out in-depth technical research in the two key areas of silicon wafer and surface passivation contact technology.
The team developed a new type of dense heterojunction passivation contact, breaking through the industry's long-standing heterojunction preparation bottleneck of 180-210 ℃, and the process temperature reached 240℃.
At the same time, the research and development team through the development of full laser graphics process and low indium, silver free metallization solution, while improving efficiency, but also to ensure the economy of BC battery technology, laying the foundation for future low-cost, efficient BC battery production.
In May 2024, Longi announced that the photoelectric conversion efficiency of its self-developed back-contact crystalline silicon heterojunction solar cell (HBC) reached 27.30%, once again breaking the world record for the conversion efficiency of single crystalline silicon photovoltaic cells. This is a breakthrough after Longi set the world record of HBC battery conversion efficiency of 27.09% in December 2023, and also represents Longi's confidence and strength in BC battery technology's high conversion efficiency and mass production process.
In the past two decades, the manufacture of crystalline silicon cells has undergone three major technological iterations. In the AL-BSF (aluminum diffused back surface field) era, the cell efficiency is less than 20%; In the era of PERC (passivated emitter back contact), the efficiency is increased to less than 25%; The TOPCon (tunneling oxide passivation contact) technology upgrade, which began last year, has made the battery efficiency exceed 25%.
Going forward, more than 26% of production battery technology will be led by BC (back contact) technology. The scientific research results of Longi point out the development direction of more than 27% of ultra-efficient battery technology for the industry: that is, promote efficiency through the infrastructure combined with heterojunction technology and BC structure.
Prospect of crystalline silicon solar cells
With the application of double-sided solar cells and high-light transmittance glass materials, the future crystalline silicon cells will be more competitive in the market. Double-sided solar cells can use the reflection of sunlight to maximize the capture of light energy. This design allows for a significant increase in the energy output of the battery, typically 10 to 20 percent more efficient than conventional single-sided batteries.
And the current global demand for clean energy is increasing, and the market demand for crystalline silicon solar cells is also growing steadily. According to the forecast, the market share of crystalline silicon cells will continue to expand in the next few years, especially in major markets such as China, the United States and Europe.
Many countries are promoting renewable energy policies, offering incentives to promote the use of crystalline silicon solar cells. This policy support provides a good environment for technology research and development and marketing promotion, and further boosts the development of the industry.
Conclusion
The application of double-sided solar cells and the use of high-light transmittance glass materials will further enhance the energy output and market competitiveness of crystalline silicon cells. Driven by policy support and incentives, this industry has ushered in new opportunities globally.
In the wave of renewable energy, crystalline silicon photovoltaic, which is considered to be the "old technology" of photovoltaic, is still vibrant and will remain so for decades to come. To ensure such a bright future, close collaboration between research and industry is essential.
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