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TOPCon Technology
1、TOPCon Technology：

TOPCon The composite structure of back oxide layer + doped polysilicon is adopted to form a good passivation contact and comprehensively improve the performance of the battery.

2、In-situ doping and non-in-situ doping: there is little difference in performance between the two options, but from the point of view of the follow-up treatment after doping, in-situ doping is a compromise option at present, which is the easiest and most stable choice for mass production and has good controllability.

3、PE and LP：

PE route has congenital problems, which can not reflect the advantages of TOPCon. Poly deposition is fast, the density is poor, and the efficiency of PE cells is low.  From the point of view of mass production, LP has met the demand, and subsequent LP will be the mainstream.

4、Comparison of technical path and difficulty between N-type and P-type:

P-type is much easier to do TOPCon, but the efficiency is not significantly improved, only about 0.5pct higher than p-type PERC. This is mainly the problem of carriers, P type carriers are holes, the transition is relatively difficult, and N type carriers are electrons, so the current mainstream choice of N type.
5、Feasibility of combining TOPCon and IBC:

This year is not only the first year of TOPCon, but also the first year of N-type silicon chip. N-type silicon chip has congenital advantages, TOPCon technology can be combined with HJT and IBC technology, but at present TOPCon is still in the stage of being able to do, rather than a good stage of technology.

Comparison between TOPCon and PERC

1. Advantages:

High efficiency: At present, TOPCon manufacturers with the highest mass production efficiency are as high as 24.8%, while the current mainstream PERC is 23.2%, which is 1.6 percentage points higher than TOPCon. It is expected that by the second half of 2023, TOPCon can reach 26.8%, PERC efficiency is around 23.5%, and the efficiency difference can reach 3.3 percentage points. Low attenuation: on the one hand, there is no case of TOPCon battery out of gear, while the current test efficiency of PERC battery drops 1 to 2 levels after a period of time; On the other hand, for the component side, TOPCon has no power attenuation, with PERC having a power attenuation of nearly 8% in the first year. Long wave response: PERC only responds well to short wave, TOPCon responds well to both. TOPCon is not affected by the weather and its power generation is guaranteed continuously, while PERC's power generation is seriously affected by the weather.

2、Disadvantages: high fixed investment: TOPCon equipment investment is 200 million yuan /GW, while PERC is 120 million yuan /GW. The process is complicated: TOPCon process has 12 steps, while PERC has 11 steps. TOPCon added three processes, deleted two processes and adjusted one process, but the new several processes are complicated and difficult to control. High non-silicon cost: at present, the non-silicon cost of TOPCon is 0.26-0.27 yuan /W, and PERC is about 0.2 yuan /W. TOPCon is 30% higher than PERC. It is expected that the cost of TOPCon is 20% higher than PERC after both costs are reduced.

Comparison between TOPCon and HJT

1、Advantages: Mature technology and good compatibility:

TOPCon's technology is relatively mature and compatible. Eight of the 12 processes are exactly the same as PERC. In the three new processes, the designed operation, process window and parameter setting are very similar to the original PERC.

Low workshop investment: TOPCon equipment investment is 200 million yuan /GW, while HJT is currently expected to achieve 300 ~ 350 million yuan /GW. Good mass production: TOPCon's operating staff and process equipment can be seamlessly connected directly from the original PERC plant, without additional training and skill upgrading. High efficiency: Currently, TOPCon is 0.4 PCT more efficient than HJT, and the efficiency gap is expected to widen by 2023. Non-silicon cost is low: TOPCon is 0.26-0.27 yuan, while HJT is currently 0.33 yuan. No battery attenuation: TOPCon has no attenuation in either the battery side or the components, but HJT's efficiency gradually degrades due to its use of cryogenic gel.

2、Disadvantages:

Long process: TOPCon has 12 steps, while HJT only has 5 steps (cleaning flocking, doping crystal silicon, conductive film, screen printing, test sorting). The longer the process flow, it means that the personnel and process complexity corresponding to the equipment increase a lot. The workshop occupies a large area: the long process process causes the need for more equipment, the land occupies a large area, and the equipment power cost of the whole engineering workshop will increase accordingly. Small reduction in silicon wafer thickness: PERC silicon wafer thickness between 170~175μm (if too much thinning, aluminum back plant stress will lead to silicon wafer strength is not up to standard), TOPCon current mainstream can do 150~155μm (to face the test of boron expansion of ultra-high temperature and severe temperature rise and drop, the subsequent should not be too thin), HJT currently mainstream laboratory batch between 110~120μm, there are very few manufacturers can achieve about 90μm. TOPCon saves about 20μm, while HJT saves about 60μm. Silicon chip size is limited: The current mainstream size of TOPCon is 182,210. At present, the resistance is relatively large, and the main resistance comes from the area of the panel and component end. HJT is limited by the process, so the size 210 can be given priority.

3、Problems encountered in HJT mass production:

Low temperature silver paste: the super low temperature of 250 degrees leads to very poor metallization of silver paste, which brings many derivative problems, the biggest one is that the welding tension of components is completely substandard. TCO film: TCO film is especially easy to aging, after aging performance decline is very serious. PERC and TOPCon battery modules typically last 15 to 20 years, while HJT's TCO films last 3 to 5 years under harsh laboratory conditions. PVD&RPD equipment: the equipment comes from semiconductor and needs precise control, but its continuous operation ability is not high.

 

 

Source: Global PV 2022-06-16 17:15 published in Shanghai