Longi’s record 27.30% efficient HBC solar cells developed using laser patterning

A Chinese manufacturer of solar modules, Longi, has revealed specific details of its heterojunction back contact (HBC) solar cell, which it developed months ago. Longi’s HBC reached an efficiency of 27.30% under laboratory conditions and was certified by Germany’s Institute for Solar Energy Research Hamelin (ISFH).

Crystalline-silicon heterojunction back contact solar cells are a promising technology. However, there are major challenges in managing charge carrier recombination to achieve high efficiency, according to Longi.

In a study, the manufacturer stated that it produced highly efficient HBC solar cells using a laser patterning technique.

Longi exploited amorphous silicon as passivating contact layers

The researchers employed amorphous silicon as passivating contact layers and utilized laser ablation as a scalable mass-production technology . This approach led to a certified efficiency of 27.09% for their HBC solar cells.

Rigorous experimental and theoretical validations were conducted for recombination loss, resistive loss, and current density loss.

Researchers maintained that the study offers multiple strategies and guidelines for optimizing structural design and resolving major contradictions within back-contact solar cells.

“Our findings indicate that recombination losses primarily arise from the hole-selective contact region and polarity boundaries. We propose solutions to these issues and establish a clear relationship between contact resistivity, series resistance, and the design of the rear-side pattern,” said researchers.

Wafer edge becomes the main channel for current density loss

The study, published in the journal Nature Communication , demonstrated that the wafer edge becomes the main channel for current density loss caused by carrier recombination once electrical shading around the electron-selective contact region is mitigated.

“With the advanced nanocrystalline passivating contact, wafer edge passivation technologies and meticulous optimization of front anti-reflection coating and rear reflector, achieving efficiencies as high as 27.7% is feasible,” said researchers.

In the study, researchers have presented the two key aspects in three-dimensional graphs and showcased the optimization space for both electrical and optical designs.

They incorporated the nanocrystalline technology from the 26.81% efficiency solar cell and addressed wafer edge effects while maintaining other parameters, and meticulous optimization of front anti-reflection coating and rear reflector to achieve an HBC solar cell with PCE surpassing 27.7%.

This is Longi’s third paper, which was published in Nature this year. The company showcased its highly efficient crystalline silicon solar cells developed via Laser-Patterned technology.

“Our Central R&D Institute has conducted in-depth research in silicon wafers and passivation technology, developing a dense heterojunction passivation contact and surpassing previous thermal constraints in heterojunction preparation,” said Longi .

The fully laser-patterned structure and a low-indium, silver-free metallization approach enhance both efficiency and economic viability for future back-contact solar cell production.

“From BSF to PERC to TOPCon, and from back-contact (BC) to heterojunction back-contact (HBC), we’ve always insisted on pushing the limits, shaping a more efficient and sustainable solar future through innovation and collaboration,” said Longi.