A team of scientists from Longi, a prominent Chinese solar module manufacturer, has made significant strides in solar technology with the development of a hybrid interdigitated back-contact (HIBC) solar cell. With an extraordinary efficiency rating of 27.81%, this advancement was first announced in April 2025 and recently validated by the Institute for Solar Energy Research Hamelin (ISFH) in Germany.
In their published study titled “Silicon solar cells with hybrid back contacts,” researchers, including Longi’s president and founder Li Zhenguo, detailed the innovative features of the HIBC cell. This new design incorporates a combination of passivated tunneling contacts and dielectric passivation layers, integrating both n-type and p-type contacts to significantly enhance performance.
The development process utilized a high-resistivity, half-cut M10 wafer along with edge passivation techniques. A unique high–low temperature process was applied to optimize the n-type contact, which combined diffusion and deposition methods to ensure effective passivation of wafer edges during production; this method, known as in situ passivated edge technology (iPET), is vital for improved cell efficiency. Additionally, an indium tin oxide (ITO) layer was employed to facilitate lateral charge transport, complemented by a multilayer stack of aluminum oxide (AlOx) and silicon nitride (SiNx) aimed at minimizing surface recombination.
Notably, the scientists achieved a reduction in phosphorus doping within the n-type polycrystalline silicon layer, which limited dopant diffusion into the active cell region, a crucial factor in enhancing conversion efficiency due to its impact on carrier mobility and electrical performance.
The innovative design features deep trenched metal fingers positioned 8 micrometers undercut to collect holes efficiently, along with selective ITO etching to reduce leakage between contacts. The thickness of the amorphous silicon layer was also refined to ensure full coverage of the p–i–n junction, promoting effective encapsulation of the n-poly-Si sidewalls. Laser crystallization, utilizing nanosecond pulses, was introduced to reduce contact resistivity while maintaining edge passivation.
The paper highlights the importance of achieving an optimal balance between passivation and conductivity, necessitating precise adjustments in the amorphous silicon layer’s thickness and optical properties, as well as meticulous calibration of laser settings.
The HIBC solar cell demonstrated exceptional performance characteristics, including a short-circuit current of 5,698 mA, an open-circuit voltage of 744.9 mV, and an impressive fill factor of 87.55%. These remarkable results are attributed to the integration of cutting-edge techniques like laser-induced crystallization and enhanced surface treatments, which have effectively lowered the ideality factor during maximum power tracking.
Looking ahead, Longi expressed optimism that the innovative techniques developed for the HIBC cell could be adapted for manufacturing heterojunction (HJT) solar cells. However, the research identified an area for potential enhancement, noting that the p-type contact exhibited 50% more resistive loss than the n-type contact, underscoring the continued need for advancements in contact resistivity to further boost overall cell efficiency.