N-type battery is a relatively mature technology in the industry with the clearest development path. There are many subdivision routes for N-type batteries, and the general conversion efficiency has exceeded the average level of 24%. The potential is huge, and the future commercialization space is very considerable. At present, the main N-type batteries can be divided into three categories: TOPCon, HJT and IBC.

TOPCon: The biggest feature of this technical route is that the theoretical photoelectric conversion efficiency is extremely high, reaching 28.7%, which is close to the limit of crystalline silicon (29.43%), which is significantly better than that of PERC (24.5%) and HJT (27.5%) [12]. Regardless of the theoretical value, the current mass production average efficiency of TOPCon batteries is 24%, which is higher than that of mainstream battery products. Another advantage of this route is that it does not require high production lines, and can be upgraded based on existing PERC production lines, which is more friendly to up-front investment and can improve the application cycle of existing production lines.

However, the shortcomings of the TOPCon route are also obvious. The production process has not yet been finalized and is very complicated. There are as many as 12 to 13 processing steps, which is much higher than the 9 for PERC cells. This results in a relatively low yield of products, and the complex production process also pushes up production costs. These factors limit the further mass production of TOPCon batteries.

HJT battery: also known as heterojunction battery or HIT, HDT, SHJ battery, is considered to be the most promising technology route for the next generation of mainstream. The average photoelectric conversion efficiency of HJT cells is about 24%, which is significantly higher than that of PERC cells, which can effectively increase power generation and dilute power generation costs. Another core advantage of HJT batteries is that there are fewer processes - the processing flow of the product is only four steps, and fewer process steps are very useful to improve the yield.

Cold knowledge: The earliest developer of heterojunction batteries was Japan's Sanyo Company, but the company later registered HIT as a trademark, making it impossible for other companies to use this abbreviation to refer to heterojunction batteries. This is why heterojunction batteries are called more often.

However, few production processes and low production costs are two different things. The biggest problem with HJT cells is that the production cost is too high: according to Solarzoom statistics, the current cost of HJT cells is about 30% higher than that of PERC cells, which is obviously unacceptable for the photovoltaic industry that puts cost reduction first [13] . The cost of HJT is due to the high requirements for raw materials and the relatively large consumption; the second is that the production line must be rebuilt because the production equipment is incompatible with the existing equipment, which greatly increases the initial cost; the third is that the product processing technology also quite complicated.