The full name of a heterojunction cell is intrinsic thin-film heterojunction cell. It is also based on the photovoltaic effect, but the PN junction is formed by amorphous silicon (a-Si) and crystalline silicon (c-Si) materials (the high and low junctions on the back side are also the same).
Structure of photovoltaic heterojunction cells
In terms of new battery technologies, photovoltaic heterojunction cells have a number of natural advantages due to their unique bifacial symmetrical structure and the excellent passivation effect of the amorphous silicon layer, such as high conversion efficiency, high bifaciality, almost no light-induced degradation, good temperature characteristics, the ability to use thin silicon wafers, and the ability to stack perovskites. In addition, their manufacturing process is relatively short, and there is a large potential for future cost reduction.
Characteristics of photovoltaic heterojunction cells
Photovoltaic heterojunction cells have high conversion efficiency, great potential for expansion, simple process and clear cost reduction path, which are in line with the development law of photovoltaic industry and are the most promising next-generation battery technology.
From the perspective of photovoltaic power plant owners, after applying HJT technology, the conversion efficiency of photovoltaic cells has increased from 22.3% to 24%, which means that for a power plant with the same land area, the annual power generation increases by about 7.6%.
Heterojunction (HJT) technology not only boasts excellent conversion efficiency but also features relatively simple manufacturing processes. Compared to PERC+ and TOPCon, which require more than 10 steps, the HJT process is quite concise. First, consistent with conventional cell processing, the surface of the mechanically cut silicon wafer is etched and texturized. Next, intrinsic amorphous silicon films are deposited on both sides of the wafer, followed by doped amorphous silicon films with opposite polarities. The next step involves preparing the TCO film, primarily through sputtering using physical vapor deposition (PVD). Finally, surface metallization is performed on top of the TCO to obtain the heterojunction cell.
Moreover, cleaning and texturing, as well as screen printing, are traditional silicon crystal cell processes. HJT's unique process lies in amorphous silicon thin film deposition and TCO film deposition. Currently, many domestic companies are actively promoting the industrialization of heterojunction cells. The highest laboratory conversion efficiency of M2-sized cells has exceeded 25%, and the leading mass production conversion efficiency is between 23.5% and 24%.
It's worth noting that a module's power output is equal to the product of the effective cell area, solar radiation intensity, and cell efficiency. Therefore, replacing PERC cells with heterojunction cells in the future will result in modules with higher power output, leading to lower cost per watt and levelized cost of electricity (LCOE) for end-users.
Compared to PERC cells, HIT cells have higher cleanliness requirements during manufacturing, necessitating a greater level of cleanliness in both equipment and workshops. Therefore, they are not compatible with traditional battery production facilities. Overall, HJT cell production equipment is incompatible with monocrystalline PERC cell production, and is also not fully compatible with other N-type cell equipment such as TOPCon and IBC.
Currently, photovoltaic heterojunction cells are in the industry introduction phase, with both new and established players accelerating the commissioning of HIT cell production lines. The global HIT cell production capacity is currently close to 3GW, but the planned capacity of major players has exceeded 16GW, making it a long-term investment.
