In the past two years, the situation of module technology has changed, and various companies have competed to carry out the "arms race" of photovoltaic technology. From size changes to solar cell technology iterations, everyone has come up with housekeeping skills.

Judging from the recent N-type technology route battle, JinkoSolar has set a new world record for the conversion efficiency of large-area N-TOPCon solar module cells, with a conversion efficiency of 25.4%. At the same time, LONGi has once again made a major breakthrough in M6 size heterojunction cells (HJT), with a conversion efficiency of up to 26.30%. As far as the current industry situation is concerned, N-TOPCon is more favored by mass manufacturers. What is supporting this technology?

1. The past and present of TOPCon solar panel technology

The core of Topcon technology lies in passivation contact. The second half of Topcon is the English abbreviation of Passivating Contact. One of the core points of improving solar cell efficiency is to continuously reduce the recombination of electron and hole pairs, from polycrystalline to single crystal, from all-aluminum backfield to PREC, step by step, continuously reduce internal consumption, and gradually reduce the internal consumption to 0.5%. The efficiency improvement rate of -0.6%/year is iterating.

M. Hermle, et al., Appl. Phys. Rev. 7, 021305 (2020).

The passivation contact of PERC can be approximately regarded as the incomplete body of TOPCon. Compared with the previous all-aluminum back field solar cell (the back of the solar cell is all aluminum except for the silver electrode), the back of the PERC solar module cell reduces the proportion of aluminum, and uses a passivation layer such as SiNx to passivate where there is no aluminum. On the back surface, the recombination of the metal-semiconductor interface is reduced, the voltage is increased, and the conversion efficiency is increased. However, the metal electrode structure of PERC solar modules cells still retains a small amount of metal-semiconductor contact area. Don't underestimate this little contact area, it is one of the dominant factors of compounding and an important factor limiting the breakthrough of PERC cell efficiency.

TOPCon's solar cell design further reduces the metal-semiconductor contact area, and goes further and further on the road of reducing recombination, constantly moving closer to the ideal solar cell, and constantly breaking through the barriers of efficiency. As shown in the figure below, the contact between the metal and the semiconductor is eliminated, and conduction is instead conducted by the tunneling effect.

P.P. Altermatt, Nature Energy 3, 718 (2018)

2. The future of TOPCon technology

According to ITRPV's forecast, N-type solar panels will gradually occupy the market share. At present, the PERC production capacity on the market is very sufficient, a large part of which has been expanded in the past two years, and the depreciation of many equipment has not been completed. At the same time, raw materials have risen this year, and many solar cell manufacturers have not produced 100% full capacity, so the profit situation is not optimistic. If you switch to heterojunction technology under the general trend of N-type in the future, it is bound to invest a considerable amount of money in equipment.

The TOPCon technology has many things in common with the current PERC technology. The old equipment is debugged, renovated and transformed, and after adding some process equipment, it can be converted into N-type solar cell production capacity at a lower cost.

ITRPV 2021

Therefore, judging from the current technical capabilities, N-type TOPCon seems to be more favored by mass manufacturers. Let's wait and see, let newer technologies and higher efficiency usher in the coming of the carbon neutral era in the future.