Fraunhofer ISE’s Head of Group Silicon Solar Cells Dr. Andreas Wolf as the keynote speaker on day 3 of the 4-day TaiyangNews High Efficiency Solar Technologies 2024 Conference, went back to the 1980s to show the evolution of the TOPCon technology calling it a ‘shivering giant.’ Back then, it was known in the semiconductor industry as the silicon insulator silicon (SIS).
He shared that the term TOPCon was coined by Fraunhofer ISE in 2013, following which its industrial implementation started around 2015 by Jolywood and LG.
Since then, TOPCon technology has come a long way to overtake PERC as the leading solar cell technology in industrial use. One of the major contributing factors among several others in its journey is the Laser-Enhanced Contact Optimization (LECO) process.
A game-changing innovation, LECO has been instrumental in increasing TOPCon cell efficiency as it decoupled the contact, and also enabled the use of aluminum-free pastes, zero busbar (0BB) approach, much lower firing temperatures, and very different boron diffusion parameters, said Wolf. Developed by a Germany based start-up, Cell Engineering, the company was fully acquired by Q Cells in 2023, and LECO is now being licensed to other TOPCon cell/module manufacturers.
At Fraunhofer ISE, the effort now is on copper plating contacts to replace silver paste consumption that accounts for a large part of the production costs. Fraunhofer ISE has started with a pilot fabrication of M10 TOPCon solar cells with electroplating using copper. The initial batch demonstrated similar efficiencies as screen printing at 24% each, but with 93% lower silver usage, he shared. Wolf is confident that plating cells will be able to be processed without silver consumption in the future - by using Sn as the capping layer for copper instead of silver.
Passivated Edge Technology (PET), developed at Fraunhofer ISE, helps recover losses by passivating the edges of shingled or half-cut cells. He said it is especially valuable for high perimeter cell area fractions. However, several manufacturers have developed their own methods to achieve these results.
Wolf also talked about TOPCon Rear Emitter (TOPCoRE) technology which replaces n-type by p-type wafers, with no front conductive layer and the efficiency can go up to 26%, as against 25.8% in TOPCon. Its major benefit is that it omits inherent recombination of the front surface which is a limitation for the current TOPCon technology. However, the challenge is related to the alignment of the structures which can be met by industrial production conditions.
In the future, Wolf sees TOPCon cells as forming a good choice for the bottom cell in a tandem structure in a multi-junction configuration.
For more presentation videos and conference summaries for all 4 days of the TaiyangNews High Efficiency Solar Technologies 2024 Conference, click here for days 1 and 2, and here for days 3 and 4.