TOPCon has become the dominant mainstream cell technology, operating at 25-26% in mass production, with industrial silicon projected to approach ~27.5%
Process innovations such as LECO, passivated edge technology (PET), and fine-line metallization have enabled further structural optimization while addressing cost and material pressures
To exceed 30% efficiency, silicon perovskite tandem architectures, especially 2-terminal designs, are seen as the next logical step for the industry
As solar cell efficiencies approach practical production limits, further improvements are becoming increasingly challenging, shifting attention from incremental refinements to more advanced architectures and tandem concepts. Research institutes play an important role in developing new device structures and helping translate laboratory progress into scalable manufacturing processes.
During the TaiyangNews High Efficiency Solar Technologies Conference 2025, Jochen Rentsch, Head of Technology Transfer at Fraunhofer ISE, outlined the evolution of crystalline silicon solar cells and highlighted the transition from single-junction optimization to tandem integration. His keynote presentation, titled Evolution and Future of Crystalline Silicon Solar Cells, combined milestones with current industrial metrics and manufacturing considerations.
TOPCon has established itself as the mainstream technology in newly installed production lines, operating at 25-26% efficiency in mass production at the cell level. According to the roadmap presented, it now accounts for the largest share of new capacity additions. JinkoSolar reported a laboratory TOPCon cell efficiency of 27.79%, closely matched by LONGi’s 27.81% BC record.
Rentsch projected that industrial silicon cells will approach a practical production limit of around 27.5% within the next 3-5 years. While laboratory efficiencies may exceed this level, further gains in mass production are expected to become incremental as silicon nears its practical ceiling.
Although HJT remains technically competitive at similar mass-production efficiencies, he noted shifting market shares and emphasized that TOPCon’s scalability and cost structure have supported its rapid industrial adoption.
As TOPCon moved into mass production, further efficiency gains required improvements in contact formation and recombination control. The optimization of its structure, however, was limited by conventional firing processes.
An important development came in 2019 with LECO (Laser Enhanced Contact Optimization), a technology jointly developed by Fraunhofer ISE and CE Cell Engineering. LECO partially decouples contact resistivity (ρc) from recombination current density (J₀), enabling thinner polysilicon layers, shallower emitter profiles, and thinner tunneling oxides. This provided additional flexibility for improving voltage while maintaining good contact properties.
Passivated Edge Technology (PET), introduced in 2020, addressed another emerging challenge that increased recombination losses in cut or shingled cells. By applying ALD Al₂O₃ at exposed edges, a significant portion of the fill-factor-related efficiency loss can be recovered.
Rentsch noted that PET can contribute up to ~0.5% absolute efficiency recovery in shingled TOPCon layouts, supporting matrix-shingle module designs without compromising performance.
Metallization continues to face significant cost pressure. Silver prices have recently exceeded $52 per ounce, while PV silver demand is projected to surpass 7.5 kilotons annually. Rentsch characterized this combination of high prices and rising demand as a structural challenge for the industry.
Screen-printing technology has evolved accordingly. The transition moved from knotless screens introduced around 2016 to laser-structured polyimide screens in 2018, and more recently to ultra-fine woven mesh screens. Industrial finger widths are now approaching 10 µm, enabling substantial silver reduction without compromising electrical performance.
Beyond fine-line printing, material substitution is gaining attention. Rentsch highlighted the ongoing development of Ag-Cu pastes, pure copper, and nickel-based pastes. Copper front-side metallization is already being demonstrated in silicon heterojunction (SHJ) cells, a shift away from silver are technically feasible under certain architectures.
In the TOPCon technology category, patent activity has increased significantly over the past 2 decades, especially between 2008 and 2018. While several Tier-1 manufacturers have started resolving disputes through cross-licensing agreements, the situation remains challenging for smaller players and new entrants.
Rentsch placed crystalline silicon within its fundamental efficiency context. The theoretical efficiency limit for single-junction silicon stands at around 29.4%, while the practical production ceiling is closer to 27%. As industrial cells approach this level, further gains within conventional single-junction architectures are expected to become incremental.
Looking beyond 2030 and toward terawatt-scale deployment, he outlined several requirements for next-generation PV technologies: efficiencies above 30%, material availability at scale, long-term stability comparable to silicon, and high-throughput manufacturing capability on the order of roughly 1,000 m² per hour. Within these constraints, Rentsch stated that tandem technology represents the only viable pathway to move beyond the silicon ceiling.
Among the architectural options, the 2-terminal (2T) configuration currently appears most promising due to its higher demonstrated efficiencies and relatively straightforward module integration. Both TOPCon and HJT were identified as suitable bottom-cell platforms for silicon-perovskite tandem designs.
For silicon-perovskite tandems, Rentsch pointed to a hybrid production route that combines wet-chemical formation of the perovskite scaffold on textured silicon, followed by annealing and evaporation of organic layers. This approach has demonstrated good conformity on textured surfaces and compatibility with industrial silicon bottom cells.
While certified fully textured silicon-perovskite tandem cells reaching 31.6% efficiency, more than 8% absolute below the theoretical tandem limit. At the same time, scaling remains the primary challenge. Most high-efficiency demonstrations are still based on small-area laboratory cells of around 1 cm². Industrial deployment would require scaling to large wafer formats such as M12.
The full presentation is available on the TaiyangNews YouTube channel here.
TaiyangNews’ latest Market Survey on Cell Production Equipment also examines recent developments in cell technologies. The report is available for free download here.