- Researchers have achieved a certified 27.27% efficiency in heterojunction back contact silicon solar cells by overcoming a major laser manufacturing challenge.
- A newly engineered front surface texture reduces laser induced damage while maintaining the precision benefits of laser patterning.
- The findings provide a practical pathway for large scale production of ultra-high efficiency silicon solar cells.
Researchers have developed a new laser processing approach that enables LONGi heterojunction back contact (HBC) silicon solar cells to reach a certified power conversion efficiency of 27.27%, addressing a long standing manufacturing challenge that has limited the industrial deployment of the technology.
The study titled ‘Harnessing and mitigating laser shock waves for 27.27% efficiency back contact silicon solar cells’, focusses on laser patterning, a key manufacturing process used to create the complex rear side structures required in high efficiency HBC solar cells. While laser processing offers exceptional precision and high throughput, it also generates powerful shock waves that travel through the silicon wafer and can damage the delicate front side passivation layers responsible for minimising energy losses.
The challenge has become increasingly important as the solar industry seeks to move beyond the efficiency limits of conventional cell architectures. Traditional aluminium back surface field solar cells have reached efficiencies of around 19%, while passivated emitter and rear cell technologies have approached 23%. More recent passivating contact technologies, including TOPCon and silicon heterojunction cells, have surpassed 26%, bringing the industry closer to the theoretical maximum efficiency of approximately 29.4% for single junction crystalline silicon.
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Among the most efficient designs currently under development, HBC solar cells have emerged as one of the leading technologies for pushing silicon photovoltaics toward the 28% efficiency threshold.
The researchers found that the primary source of damaging shock waves originates from the laser ablation of a silicon nitride layer on the rear side of the solar cell. Through detailed simulations and microstructural analysis, the team identified what they describe as an “explosive removal” mechanism.
During laser processing, the underlying polysilicon layer rapidly heats and vaporizes, creating enough pressure to mechanically eject the overlying silicon nitride film. While this process effectively creates the required rear side patterns, it simultaneously generates shock waves that can degrade the front side surface structure and reduce passivation quality.
To address this issue, the team developed a redesigned front side texture consisting of submicron pyramids with rounded tops. Acting as a mechanical energy dispersing structure, the modified texture reduces stress concentrations caused by shock waves and prevents damage to the front side passivation layer.
Simulation results showed that conventional pyramid textures experienced localised stresses exceeding the yield strength of silicon, increasing the risk of microcrack formation and long term damage. In contrast, the rounded top pyramid design reduced peak stress levels below the silicon yield threshold, significantly improving resistance to laser induced shock effects.
The researchers also carried out extensive microscopic investigations of laser processed regions. These studies revealed that laser interaction with the silicon nitride layer causes mechanical fracture, localised melting, crystalline transformation and void formation within underlying layers. The findings provided critical insight into how laser generated shock waves propagate through the wafer and affect device performance.
By combining precise rear side laser patterning with a shock wave resistant front side texture, the researchers successfully preserved passivation quality while maintaining the manufacturing benefits of laser processing.
According to the study, the work resolves a fundamental contradiction in laser based solar cell manufacturing by allowing manufacturers to harness the benefits of laser generated shock waves for patterning while minimising their harmful effects on sensitive device structures.
The researchers believe the approach offers an industrially viable route to the next generation of ultra-high efficiency silicon solar cells and could support wider commercial adoption of HBC technology as the photovoltaic sector continues its push toward higher performance and lower cost renewable energy generation.
Link to the full paper HERE
Author: Bryan Groenendaal
