After a short-lived show around 2010, the cast single crystal is now making a comeback, and it is coming.
The so-called cast single crystal is an ingot furnace, which uses the seed crystal to perform crystal growth in a directionally solidified manner, and produces a large ingot of the ingot single crystal, which is also called a quasi-single crystal or a single crystal. In the current mainstream manufacturing process, casting is actually a traditional polycrystalline production method.
"In fact, the current dispute between single and polycrystalline is the competition between Czochralski technology and casting technology. Casting single crystal is skillfully low cost, low energy consumption, large size advantage of casting technology and high efficiency and high quality of single crystal. The advantages are combined.†Academician Yang Deren of Zhejiang University believes that casting single crystals draws the advantages of both casting and single crystal.
After nearly a decade of accumulation, this time, will the cast single crystal technology that has come back to the test stand the test of the market? Who will eat the market?
Casting single crystals that have come back. Looking back at the history of casting single crystals, you will find that this is not a completely new technology. According to Dr. Wan Yuepeng, Chief Technology Officer of GCL-Poly, as early as 2005-2008, BP Solar cast single crystal (Mono2) demonstration power station application, the efficiency is about 17-18.0%, close to the straight pull single crystal, but there is no scale Application; By 2010, domestic companies such as Jingao, Qihui, LDK, GCL, and Tianhe have introduced cast single crystal products, but by 2013, high-efficiency polycrystalline products have arisen, and casting single crystals have basically been abandoned by the industry. .
In the stage of technology exploration, some technologies are gradually admired and become mainstream. Some directions are abandoned by the market and there are bound to be reasons for their anachronism.
Wan Yuepeng believes that there are four reasons for the lack of large-scale application of cast single crystals in the past. First, there was a large proportion of crystal flowers after the alkali-making of the products at that time. The appearance of the components became the main obstacle accepted by the market; The problem of dislocation in technology is not solved, the battery efficiency distribution is very wide, there are 10-20% inefficient batteries; the third is the low proportion of all single crystal (<30%), there are a large number of 2, 3 types of tablets (large crystal flowers, high position Wrong); Fourth, the stitching seam causes chromatic aberration on the silicon wafer.
In the photovoltaic industry, which is increasingly pursuing product efficiency, the above four reasons are also doomed to the failure of casting single crystal. It’s not a day’s work to make a comeback today.
In fact, Poly GCL, which is the main pusher of polycrystalline, has been casting single crystals as one of the technical reserves. With the increase in the market share of single crystals, the mainstream status of polycrystalline has gradually declined. It is the good time for GCL-Poly, which has a large number of ingot furnaces, to introduce single crystals.
Dr. Wang Chen, General Manager of GCL-Poly Technology Management Department, said at the 4th Symposium on Photovoltaic Power Generation Design, Engineering and Equipment Selection, “Traditional polycrystals are weaker than single crystalsâ€. He believes that casting single crystal is the direction that ingot technology must go.
What is the efficiency of single crystals with the cost of polycrystals?
Such a high-profile announcement of the return of casting single crystal, GCL has made a lot of effort in recent years. New thermal field design, segmented heating to increase symmetry, increase convection, increase single crystal ratio, reduce dislocations, etc.; new seed splicing technology can avoid dislocations generated by seams; original seed crystal reuse Technology can further reduce costs; wafer wafer sorting can better solve component appearance problems. For the above four reasons, GCL has overcome one by one.
In terms of appearance, GCL said that Xin single-crystal silicon wafers are cut with diamond wire, and the appearance is similar to that of conventional polycrystalline silicon wafers. There is no significant difference between the use of alkali-based velvet and the straight-drawn single crystal. In addition, through the Hennecke automatic sorting line to strictly control the crystal flower problem, the silicon wafer with a single crystal area of ​​less than 99% was selected as three types of wafers, accounting for about 10%.
According to Dr. Zhang Wei, the chief technology officer of GCL, in the research and development phase from September to October 2018, it was found that the use of the alkali-based velvet process for the three types of tablets would have serious appearance problems, and the use of wet black silicon velvet could perfectly solve the problem. problem.
In terms of dislocations, Wang Chen said, "Compared with single crystal, although the ingot single crystal is not a perfect crystal, the proportion of dislocations is much lower than that of polycrystalline, which is very close to the single silicon after cutting. Crystal products."
From a technical point of view, dislocations cause a decrease in the life of the minority, which reduces battery efficiency, which is one of the most deadly weaknesses of ingot single crystals.
However, Wan Yuepeng explained that the casting single crystals have significantly reduced the dislocations after the growth of the crystal growth technology. At present, the power output of the 72-piece module of Xin single crystal is mainly 380Wp, which is lower than that of the straight-drawn single crystal module of the same size and PERC process. 5Wp.
According to Zhang Wei, after continuous improvement, the current single-crystal EL degradation rate is 2.29%. The situation of obvious EL dark lines in the early low-end position has basically disappeared. The main defect is the grain boundary line, accounting for 1.25%. A small amount of unqualified fluff, accounting for 0.05%.
In addition, casting a single crystal to attenuate less than a single crystal PERC as its highlight. The oxygen content of the silicon wafer is <6 ppm, which is significantly lower than that of the straight pull single crystal of 12-13 ppm, and the LID and LeTID are lower than that of the Czochralski single crystal. However, Zhang Wei introduced that the light decay data of Xin single crystal is slightly worse than that of the crystal. It is suspected that the main single crystal sintering temperature is higher than that of the crystal. Polycrystalline LeTID control has mature industrialization technology, and Xin single crystal needs further optimization.
In terms of cost, GCL said that the cost of casting single crystal is slightly higher than that of conventional polycrystal, but it is lower than single crystal. In the future, the casting material can be further reduced by the gradual increase of the loading amount and the seed crystal recycling technology. The cost of crystal, while the application of scale will inevitably lead to a large-scale reduction in costs.
In terms of energy consumption, the power consumption per kilogram of cast single crystal is 20 degrees lower than that of Czochralski single crystal, and it is converted into electricity consumption of 0.06 degrees per watt.
In terms of equipment, there is currently no ingot casting single crystal equipment that can be directly used on the market, which needs to be self-reformed. It is necessary to invest a small amount of new equipment for the life and defect detection of cast single crystal ingots, mainly to increase the end face life detection and position. Wrong detection and crystal flower module.
To sum up, cast single crystal is a product between traditional polycrystalline and high efficiency single crystal. However, there seems to be a certain gap in the efficiency of single crystals from the cost of polycrystals.
How far is the “single†cast single crystal from a large-scale application?
According to current news, almost all of the information related to casting single crystals comes from GCL and its allies. According to photovoltaics, there are not many manufacturers of cast single crystal products, and a battery manufacturer is about to mass production, but the products are only supplied to GCL.
Some insiders have revealed to photovoltaics that if casting single crystals can be done well, it is definitely a competitive advantage for Czochralski single crystals. Now the key is to get approval from samples and battery factories.
GCL announced that the number of furnaces has been increased, the amount of single-loading has increased, and the total capacity has been continuously increased. In 2019, the annual production capacity of single crystals can reach 8-10GW.
Although the production capacity is rapidly increasing, it seems to be verified whether it can adapt to the current fast-growing PV industry as an improved technology that has not yet been applied on a large scale.
Any new thing needs to go to the market requires a process, so how to cast a single crystal is accepted by the market, wait and see
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