A team of researchers at Germany-based Fraunhofer Institute for Solar Energy Systems ISE reported having achieved a record conversion efficiency of 26.0 per cent for both-sides contacted silicon solar cells.

In the recently published Nature Energy articleDesign Rules for High-Efficiency Both-Sides-Contacted Silicon Solar Cell with Balanced Charge Carrier Transport and Recombination Lossesthe solar cell researchers led by Dr. Armin Richter show that it is also possible to achieve the highest efficiencies for this type of solar cell, which have been established as the industry standard and have become the preferred choice in industrial production due to their lower complexity.

The basis for the record cell  is the Tunnel Oxide Passivating Contact (TOPCon) technology developed at Fraunhofer ISE, which combines the advantages of very low surface recombination losses with efficient charge carrier transport.

While industrial standard cells have a pn junction on the front side, the pn junction in the record cell was formed on the back side as a full-surface TOPCon contact. Thus, the full-surface boron doping on the front side was no longer required so that only a local boron diffusion directly under the front-side contacts was implemented.

This TOPCon Rear Emitter (TOPCoRE) solar cell allows higher voltages and higher fill factors than cells with a collecting emitter on the front side.

With this cell design, the wafer can be better utilized for charge carrier transport and the front side is more effectively passivated, for which aluminum oxide is used.

Detailed power loss analysis shows that this cell generally compensates for and minimizes both electron and hole transport losses as well as transport and recombination losses.

Prof. Stefan Glunz, Division Director of Photovoltaics Research at Fraunhofer ISE explained:

“Based on a systematic simulation-based analysis, we were able to derive some fundamental design rules for future high-efficiency silicon solar cells above 26 percent efficiency. Both-sides-contacted solar cells have the potential to reach efficiencies up to 27 percent and thus surpass the previous world record for silicon solar cells.”

Source: Press release by Fraunhofer ISE. Photo credit: © Fraunhofer ISE. The TOPCoRE solar cell achieved 26 percent efficiency, a new world record for both-sides-contacted solar cells.

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