EPJ PV Highlight - Advanced TOPCon solar cells with patterned p-type poly-Si fingers on the front side and vanishing metal induced recombination losses

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Published on 04 July 2025

Advanced TOPCon solar cells with patterned p-type poly-Si fingers on the front side and vanishing metal induced recombination losses

TOPCon solar cells have rapidly become the new industrial standard in solar cell production, highlighting the benefits of applying a contact passivation scheme based on a thin interfacial oxide and a highly doped polycrystalline silicon (poly-Si) layer. Additionally, the introduction of the laser-enhanced contact passivation (LECO) process has brought significant gains in efficiency by further improving contact and surface passivation. Additionally, it allows reducing the poly-Si layer thickness and eliminates the need for aluminum containing metal pastes that have been associated with certain solar cell degradation mechanisms.

For further efficiency improvements beyond such standard TOPCon solar cells, interdigitated back contact (IBC) solar cells are a viable contender. However, considering the current market dominance of both-sides contacted solar cells, further upgrades to the TOPCon cell architecture will also be of interest in the near future. We therefore explore the possibility of integrating p+ poly-Si passivated contacts locally under the front metallization of TOPCon solar cells and present a lean process flow to achieve this goal. Notably, our approach only employs process equipment that is commonly used in industrial mass production of solar cells. Structuring the p+ poly-Si layer is needed to minimize parasitic absorption of light at the cell’s front side and can be achieved using a unique patterning technique consisting of local dopant activation with a green nano-second laser and conventional alkaline texturing. The paper shows that the application of local p+ doped poly-Si contacts allows to achieve vanishing metal-induced recombination loss and hence a higher open circuit voltage than for a standard TOPCon reference group without passivated contacts at the front side. Furthermore, the paper proves – to our knowledge for the first time ever – that LECO also leads to contact improvement on p+ doped poly-Si. Previously this was only reported for phosphorous and boron doped mono-crystalline emitters for PERC and TOPCon cells, respectively, and for n+ doped poly-Si. Finally, the paper also critically reflects on the limitations of the technology and on the challenges that have to be solved for it to be an economically viable upgrade to existing TOPCon lines.