Unlocking Peak Power: Longi Reveals the Engineering Behind a World-Record 27.81% Efficient Silicon Solar Cell

In a landmark achievement for renewable energy, Chinese solar giant Longi has unveiled the intricate technical details behind its record-shattering silicon solar cell. First announced in April 2025 and certified by Germany’s Institute for Solar Energy Research Hamelin (ISFH), this breakthrough pushes the efficiency of silicon photovoltaics to an unprecedented 27.81%.

Published in the esteemed journal Nature, Longi’s scientific paper provides the first comprehensive explanation of its hybrid interdigitated back-contact (HIBC) solar cell. This revelation moves beyond initial announcements, offering a deep dive into the architectural redesign and material innovation that made this world record possible.

A Hybrid Approach to Unprecedented Efficiency

The core of Longi’s innovation lies in its hybrid back-contact design, which ingeniously places both n-type and p-type contacts on the cell’s rear surface. This eliminates metal shading on the front, allowing for maximum light absorption – a significant departure from standard cells. To further optimize performance, the design integrates passivated tunneling contacts and dielectric passivation layers, drastically reducing recombination losses and boosting the conversion of light into usable charge.

Key to this advanced structure is a high-resistivity, half-cut M10 wafer, specifically treated with edge passivation. This crucial step, known as in situ passivated edge technology (iPET), prevents carrier loss at the edges, a common vulnerability in many solar cell designs. Furthermore, the team developed a specialized n-type contact using a unique two-step, high-low temperature fabrication sequence, which simultaneously manages diffusion and deposition while passivating wafer edges during manufacturing.

On the cell’s textured front surface, Longi engineered a multilayer stack of aluminum oxide (AlOx) and silicon nitride (SiNx). This sophisticated combination refines light handling and suppresses electron-hole recombination, complemented by an amorphous silicon (a-Si) layer for overall passivation and contact formation.

Precision in Materials and Manufacturing

The quest for peak efficiency demanded meticulous fine-tuning of materials and processes. Longi’s researchers strategically reduced phosphorus doping in the n-type polycrystalline silicon (n-poly-Si) layer by an order of magnitude. This precise control curbed excessive dopant diffusion, preserving carrier lifetimes and enhancing contact behavior.

The design also incorporates 8-micrometer-deep metal trenches for efficient hole collection, alongside selectively etched indium tin oxide (ITO) regions. These ITO regions prevent leakage pathways between alternating n-type and p-type contacts and facilitate lateral charge transport across the rear surface.

Further advancements involved increasing the thickness of the amorphous silicon layer to ensure comprehensive coverage of the p–i–n junction and full encapsulation of the n-poly-Si sidewalls. To counteract the increased resistivity that typically accompanies thicker a-Si, Longi employed a pulsed green nanosecond laser to crystallize the layer. This innovative method maintained crucial edge passivation while significantly lowering contact resistance, highlighting the delicate balance between optical passivation and electrical conductivity achieved through precise control of a-Si thickness, laser fluence, and pulse duration.

The Future of Solar: Record Performance and Scalability

The culmination of these innovations is a solar cell that delivered a short-circuit current of 5,698 mA, an open-circuit voltage of 744.9 mV, and an impressive fill factor of 87.55% on an active surface area of 133.63 cm². This outstanding performance is attributed to the synergistic effect of laser-induced crystallization, in situ edge passivation, and enhanced surface treatments, resulting in an ideality factor below 1 at the maximum power point – indicating near-ideal diode behavior and minimal losses.

Crucially, Longi emphasizes that these groundbreaking techniques are compatible with existing heterojunction (HJT) manufacturing lines. This compatibility suggests a clear roadmap for industrial scalability, paving the way for mass production of ultra-high-efficiency solar cells that could significantly accelerate the global transition to clean energy.

While the p-type contact still presents approximately 50% higher resistive losses compared to its n-type counterpart – indicating an area for future refinement – Longi’s HIBC device sets a new global benchmark. It not only showcases the incredible potential of advanced material science and precision manufacturing in pushing silicon solar cell efficiency closer to theoretical limits but also provides a powerful blueprint for the next generation of renewable energy technologies.

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