1. TOPCon battery - the mainstream technology of a new generation of battery
TOPCon battery is tunnel oxide passivated contact battery. Mainstream TOPCon battery uses N-type silicon wafers. First, a 1-2nm ultra-thin oxide layer is prepared on the back of the cell, and then a polysilicon layer is deposited on the oxide layer, followed by annealing and crystallization to enhance the passivation effect.
Principle of TOPCon battery:
The core structure of TOPCon battery is composed of an ultra-thin silicon oxide layer and a heavily doped polysilicon layer on the back of the battery, which together form a passivation contact structure. The ultra-thin oxide layer allows many electrons to tunnel into the polysilicon layer, and at the same time blocks the recombination of minority electrons. Then the electrons are transported laterally in the polysilicon layer and collected by the metal. It greatly reduces the metal contact recombination current, increases the open circuit voltage and short circuit current of the battery, and thus improves the battery efficiency.
2. Core advantages of TOPCon battery
TOPCon battery has the advantages of high conversion efficiency, compatibility with existing PERC production lines, and excellent battery parameter performance. Currently PERC is facing bottlenecks in efficiency improvement, and HJT investment return cycle/cost reduction still needs time to be optimized. TOPCon battery is currently one of the photovoltaic cell technologies with the most room for development.
Advantage 1: high photoelectric conversion efficiency and great potential for efficiency improvement. There is a huge potential for improving the efficiency of TOPCon battery. The current mass production efficiency of TOPCon battery is around 24.5%-25%, and the highest laboratory efficiency reaches 26.1%. TOPCon battery efficiency improvement path is clear. Compared with the theoretical limit efficiency of 28.7%, the mass production efficiency of TOPCon battery still has a lot of room for optimization, and the efficiency improvement path is clearer.
Advantage 2: TOPCon battery can be upgraded based on PERC production lines, and the investment in single GW equipment is lower than that of HJT. TOPCon is compatible with PERC production lines and can be upgraded based on PERC production lines.
Advantage 3: TOPCON battery parameters have excellent performance, which can increase the full-cycle power generation. High double-sided rate: The double-sided rate of TOPCon battery can reach 80%+, and that of PERC is about 70%. Low attenuation rate: Phosphorus-doped substrate of N-type cell silicon, no boron-oxygen pair formation recombination center for electron capture loss, almost no light-induced attenuation. The decay rate of TOPCon modules is about 1% in the first year (PERC is about 2%), and the average annual decay rate after the first year is about 0.4% (PERC is about 0.45%).
3. TOPCon battery premium is beginning to appear
Premium side: It is mainly formed by the increase in power generation brought about by BOS cost dilution and low attenuation. According to PVInfolink’s quotation, the current price of TOPCon battery is about 1.41-1.45 RMB/W, which is higher than that of traditional PERC batteries, and has begun to be cost-effective compared with the rise in cost.
- The premium brought about by BOS cost dilution is about 0.03 RMB/W;
- The premium generated by the increase in power generation brought about by the low decay rate.
Cost side: mainly includes silicon cost and non-silicon cost. Currently, the cost of TOPCon battery is about RMB 0.06/W higher than that of PERC, mainly due to the consumption of silver paste and equipment depreciation. To further reduce the cost of TOPCon battery, it will mainly focus on four aspects: silicon wafer thinning, silver paste consumption, equipment depreciation, and efficiency improvement:
● Silicon wafer: develop towards large size and thin slice. At present, the thickness of silicon wafers used in PERC and TOPCon cells is about 150-155 μm, and the cost of silicon wafers can be reduced by further thinning.
● Silver paste: Similar to PERC, TOPCon battery uses high-temperature silver paste, but the consumption per chip is around 120mg, which is higher than PERC and lower than HJT. In the future, with the maturity of multi-busbar technology, the replacement of materials such as silver-aluminum paste on the back, and copper electroplating, the cost of silver paste will further decline.
● Equipment depreciation: At present, the investment in TOPCon battery single GW equipment is about 180-230 million RMB. In the future, with the improvement of equipment efficiency and the localization of core components, the price of equipment is expected to decline, so there is still room for the depreciation amount brought about by equipment investment to decline.
● Improve conversion efficiency: The current mainstream TOPCon battery efficiency is between 24.5 and 25%, and there is still a lot of room for improvement in the future. Efficiency improvement paths include: metal gate line width optimization, metal composite improvement, rear light absorption optimization, passivation optimization, metal contact optimization, silicon wafer quality, etc.
4. TOPCon battery equipment - multiple technologies coexist
The preparation process of TOPCon battery includes cleaning texture, front boron diffusion, BSG removal and back etching, oxide layer passivation contact preparation, front aluminum oxide deposition, front and back silicon nitride deposition, screen printing, sintering and test sorting. From the perspective of technology path, the LPCVD method is the mainstream process for mass production at present, and it is expected that the PECVD route is expected to become a new direction in the future.
Among them, the preparation of the passivation structure of the oxide layer is the main process added to the TOPCon battery on the basis of the PERC, and it is also the core process of the TOPCon battery. The process route is roughly divided into three types:
- LPCVD intrinsic + phosphorous expansion
- PECVD in-situ doping
- PVD in-situ doping
Overall, the LPCVD process route has the highest maturity and is currently the mainstream process for TOPCon battery preparation in photovoltaic battery companies in the world. In the future, with the continuous improvement of PECVD technology and the continuous improvement of process stability, PECVD is expected to gradually become the mainstream due to its lower cost. LPCVD was the earliest and most mature, with high film quality and high production capacity, but there are more serious winding plating problems, and the cost of consumables such as quartz tubes is relatively high.
The problem of PECVD winding plating is slight, and the cost of consumables is low because there is no need to use quartz tubes. However, the uniformity of film formation is not stable at present, and the density of film formation is not high. It is expected to benefit from technological iteration and become the mainstream technology in the future. PVD does not have the problem of winding plating, but the investment in equipment is high, the quality of film formation is unstable, and the process route needs to be further matured.
5. TOPCon battery competition landscape
Compared with the traditional PERC process, the core of the TOPCon battery adds boron diffusion, and the preparation of the tunneling layer and p-Poly layer, and the rest basically continues the basic configuration of the PERC production line. The core incremental equipment includes diffusion furnace, laser SE equipment, LPCVD/PECVD equipment. Compared with PERC, the technical barriers of TOPCon battery equipment are higher, and the cost optimization space is larger. Only the companies with the best equipment can win in the end, and the industry may become a competition pattern of several oligopoly.
- Common traditional equipment with PERC: including wet process equipment, most dry process equipment, back-end metallization equipment, and automation equipment.
- CVD equipment for preparing tunneling layer and p-Poly layer: At present, the production capacity of the market is mainly LPCVD equipment, and Laplace has an absolute leading market share in the LPCVD field. Starting from the second half of 2022, TOPCon battery market expansion will begin to gradually see orders for tubular three-in-one PECVD paths.
- Laser SE equipment: use the high temperature of the laser to diffuse the boron source in the BSG layer to the silicon wafer to form a heavily doped region, and the company accelerates the layout.