①This is a typical double-sided cell. A bifacial solar cell is a solar cell that can receive light and generate photogenerated voltage and current on both the front and the reverse side of the silicon wafer. It is an improved version of P-PERC technology.
②N-PERT can achieve mass production with easy technical difficulty and less investment in equipment. However, it has no cost-performance advantage over double-sided P-PERC and has proven to be an uneconomical technology route.
2. HIT/HJT Cell
The VOC open circuit voltage is increased by adding a layer of amorphous silicon heterojunction. This increases the conversion efficiency of the cell.
① The laboratory conversion efficiency of pure heterojunction cells has exceeded 25%. Superimposed IBC technology becomes HBC cell and the conversion rate increases to 26%. If HIT is combined with the previously mentioned thin film calcium titanite cells, a lab conversion efficiency of 28% can be obtained.
②Short production process, good temperature coefficient, basically no light decay, high double-sided rate and many other advantages.
①The battery production equipment is not compatible with the conventional crystalline silicon cell route. If a PV enterprise chooses heterojunction technology, it cannot realize the mass production of the new technology by modifying the existing cell production line. Then they can only invest in the construction of a brand new production line, resulting in high investment costs for the enterprise in the initial promotion.
② The degree of localization is low. Without reliable localized equipment, it is naturally difficult to reduce the cost.
It is understood that, at present, heterojunction production equipment accounts for the bulk of the production cost of heterojunction. Take the core equipment PECVD for example: all along, the main manufacturer of the equipment is the German enterprise Meyerberg and other foreign enterprises. This undoubtedly increases the pressure on domestic enterprises to promote heterojunction technology.
This will largely reduce the initial investment threshold for heterojunction production lines, laying a solid foundation for heterojunction to become the mainstream choice for PV companies to expand production.
Advantages of the tunneling oxide layer passivation contact technology developed on the basis of the N-cell process：
①TOPCon is compatible with existing PERC production lines. It is compatible with the existing production line well enough. It is also possible to switch to TOPCon production line from the current mainstream PERC production capacity. Compared with. Compared with heterojunction, which requires a complete rebuild of the production line, the TOPCon route is more easily accepted by existing cell factories.
②The technology can greatly reduce the surface compounding and metal compounding on the back side, and therefore substantially improve the VOC and conversion efficiency of N-type cells.
It is the TOPCon battery with poor light collection on the back side, and the difficulty of mass production is very high.
Advantages: The highest efficiency, can reach more than 24%.
Disadvantages: High technical difficulty, high investment in equipment, high cost, mass production has not been achieved in China.
|Item||HIT||Conventional monocrystalline||Conventional polycrystalline||Monocrystalline PERC||Black silicon polycrystalline||N-PERT|
|Mass production efficiency||23-24%||20-50%||18-70%||22-23%||20-80%||23-24%||23-60%|
|Low light response||High||Low||Low||Low||Low||High||High|
TOPCon has the theoretical limit of the highest efficiency, but unfortunately, the back of the collection of light is too poor.
At present, HIT and TOPCon are two choices, and the industry is not completely lopsided. Let’s wait and see, don’t be led by the market rhythm.
5. P-type cells and N-type cells
According to the different substrates, silicon wafers can be divided into P-type cells and N-type cells. p-type cells are cells with n+/p structure prepared in P-type silicon wafers, and P-type cells use a phosphorus diffusion process. The main representatives are the early aluminum backfield cells and the current mainstream PERC cells, with an ultimate conversion efficiency of 24.5%. before 2015, BSF cells occupy 90% of the market, in 2016 PERC cells began to take off, and by 2020 PERC cells account for more than 85%. p-type cells process is relatively simple, and low cost but faces efficiency improvement bottleneck.
N-type cell structure optimization, with higher efficiency potential. n-type cells use a boron diffusion process, p+/n structure on N-type silicon wafers, the main representatives of TOPCon and HJT. compared with P-type cells have the advantages of a high conversion rate, low-temperature coefficient, high bifacial rate, and high carrier life. the limit conversion efficiency of TOPCon and HJT is 28.7% and 27.5%, respectively. The ultimate conversion efficiencies of TOPCon and HJT are 28.7% and 27.5% respectively, far exceeding the current 24.5% ultimate efficiency of mainstream PERC cells.
N-type cells use higher quality silicon wafers and increase the SE process. On one hand, N-type cells require higher quality silicon wafers compared to P-type cells. Lower resistivity, lower oxygen content, and higher oligon lifetime are required. On the other hand, N-type cells also add SE process to effectively improve the efficiency. SE process, i.e. selective emitter technology, is doped with high concentration in the electrode contact area and low concentration in the light absorption area to reduce the contact resistance near the emitter.
Advantages of N-type cells over P-type cells.
(1) High conversion efficiency. Currently, the average mass production efficiency of PERC stacked with SE technology is 22%-22.4% for P cells, 22.4%-23.1% for TOPCon, and 23%-23.6% for HJT in N cells.
(2) High bifacial rate. P-type PERC cell bifacial rate is about 75%, while N-TOPCon bifacial rate is over 85% and N-HJT bifacial rate is over 95%.
(3) Low-temperature coefficient, N-type cell temperature coefficient is lower than P-type, suitable for higher temperature application scenarios such as Africa, the Middle East, and other regions with better irradiation conditions.
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