Heterojunction is a type of solar cell. A solar cell is a device that uses the photovoltaic effect to convert solar energy into electrical energy. Its core is a semiconductor PN junction. (How does solar energy generate electricity? What is a PN junction? Search "Photovoltaic Hybrid Theory" on Baidu) According to different base materials, they can be divided into crystalline silicon cells and thin film cells. Among them, crystalline silicon cells are relatively mature and are the mainstream in the current market. The most critical indicator of solar cells is conversion efficiency. Before 2015, the market was dominated by aluminum backfield (BSF) cells, with an efficiency of 19%. PERC (passivated emitter and rear cell) cells began to be used in 2015, with an efficiency of 21.5%. At present, the photovoltaic industry mostly uses PERC cells or various plus versions of PERC. With the development of various plus versions of PERC batteries, no matter what you do, you cannot break through the 22% efficiency. Everyone is beginning to pay attention to the next generation technology-heterojunction batteries. Heterojunction is a special PN junction composed of amorphous silicon and crystalline silicon. It is an N-type cell in which a thin film of amorphous silicon is deposited on crystalline silicon. HIT (heterojunction with intrinsic thin film) battery was first successfully developed by Japan's Sanyo Company in 1990. Because HIT has been registered as a trademark by Sanyo, it is also known as HJT, HDT or SHJ. Don't get confused when you see these words, they all mean the same thing.