What is the process flow of TOPCon cells

Cleaning and texturing: After the silicon wafer is cut, its edge is damaged, the lattice structure of silicon is destroyed, and the surface is seriously compounded. The main purpose of cleaning and texturing is to remove surface damage and form a surface pyramid light-trapping structure to increase light absorption and improve the minority carrier lifetime.
Boron diffusion process: The main function is to prepare PN junctions. Due to the low solid solubility of boron in silicon, high temperature and longer time are required for diffusion. Boron diffusion is usually completed at a higher temperature, exceeding 1000°C, and the cycle time of boron diffusion is 150 minutes compared with the 102-minute cycle required for phosphorus diffusion.
Doping process: Form a heavily doped area to improve the photoelectric conversion efficiency. TOPCon cells superimposed with SE technology can theoretically achieve an efficiency increase of 0.5%, and in actual mass production, it can achieve an efficiency increase of 0.2~0.4%. The doping process can use lasers for grooving or doping. The specific methods include two boron diffusions + laser grooving, two boron diffusions + laser doping, and one laser boron doping.
‌Etching process‌: The main function is to remove BSG and back junction. The diffusion process will form a diffusion layer on the surface and periphery of the silicon wafer. The peripheral diffusion layer is prone to short circuit, and the surface diffusion layer affects the subsequent passivation, so it needs to be removed.
‌Preparation of tunneling oxide layer and polysilicon layer‌: Deposit a 1-2nm tunneling oxide layer on the back, and then deposit a 60-100nm polysilicon layer to form a passivation structure. The main routes include LPCVD, PECVD, and PVD, with LPCVD being the main method at present.
‌Preparation of back anti-reflection film‌: Prepare an anti-reflection passivation film layer on the back of the battery to increase the absorption of light. At the same time, the hydrogen atoms in the formation process of SiNx film have a passivation effect on the silicon wafer.
‌Front aluminum oxide plating‌: Deposit an aluminum oxide film layer on the front of the silicon wafer, and form a front passivation effect together with other film layers.
‌Preparation of front anti-reflection film‌: The front anti-reflection film and the back work together to increase the absorption of sunlight, reduce optical losses, increase photocurrent, and thus improve conversion efficiency.
TOPCon cell technical advantages and application prospects: TOPCon cells have the advantages of low attenuation, high bifaciality, and low temperature coefficient. Its manufacturing process is very similar to PERC/PERT solar cells, and manufacturers only need to make a small investment to upgrade existing production lines. TOPCon cell technology has the potential to develop rapidly and can occupy a place among existing PERC/PERT photovoltaic module manufacturers in the market.