EPJ PV Highlight - Approaches for reducing metallization-induced losses in industrial TOPCon solar cells

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Published on 24 November 2025

Approaches for reducing metallization-induced losses in industrial TOPCon solar cells

The tunnel oxide passivating contact (TOPCon) structure has been widely accepted in industrial manufacturing, making it the dominating solar cell structure in 2025. One key to further increase conversion efficiency of such solar cells is minimizing carrier recombination at metal-semiconductor interfaces.

For that purpose one could lower the firing set temperature, or one could increase the thickness of dielectric layers between crystalline wafer and metal paste; however, both approaches typically result in increased contact resistivities and thus a lower fill factor in the solar cell. Also, a too low firing temperature leads to an incomplete hydrogenation of the interfaces, negatively affecting the pseudo-fill factor of the solar cells. Recently, the introduction of laser enhanced contact optimization after contact firing has allowed for decoupling recombination and contact properties to some extent, which results in both high fill factors and high open circuit voltages at the same time. To exploit the full potential of contact optimization, the paper speculates on the need for improved hydrogenation of interfaces, which contradicts the wish to decrease firing temperatures for reduced carrier recombination at metal-semiconductor interfaces. The implementation of an additional tube furnace annealing step after dielectric surface passivation and before screen-printing of the metal contacts, leads to improved passivation properties in lifetime samples, so that the thermal budget during contact firing can be optimized to minimize contact resistivities. Overall, contact optimization allows for TOPCon solar cell efficiencies of 24.1%, for a traditional approach without additional annealing step, and applying an AgAl front side metallization paste. A comparison of Ag and AgAl front side metallization pastes reveals a higher open circuit voltage for the Ag paste, at the drawback of an increased contact resistivity, which needs to be addressed by optimization of the paste composition, given the current trend in industry towards emitters with sheet resistances of around 400 Ω/sq and reduced dopant concentrations.