A group of researchers from Chinese PV manufacturer Longi and China’s Yangzhou University has developed a new manufacturing technique to mitigate laser shock waves in the production of heterojunction (HJT) back-contac (BC) solar cells in an effort to reduce potential damage.
“Our work not only addresses a major contradiction in laser-based manufacturing but also offers a practical, industry-ready route toward ultra-high-efficiency photovoltaics,” corresponding author Lvzhou Li told pv magazine. “Laser processing plays a central role in modern photovoltaic manufacturing, providing benefits in throughput, precision, and patterning flexibility. However, at high energy densities, the interaction between ultrafast laser pulses and silicon can trigger non-thermal processes that produce instantaneous, high-pressure shock waves.”
Laser-induced shock waves can damage solar cells by generating extremely rapid, localized pressure spikes within the silicon lattice. These stresses can exceed the material’s mechanical limits, leading to microcracks and defect formation. Such damage degrades carrier transport and reduces the overall efficiency and reliability of solar cells.
In the paper “Harnessing and mitigating laser shock waves for 27.27% efficiency back contact silicon solar cells,” published in Solar Energy, Li and his colleagues specifically addressed the degradation of front-side passivation and texture caused by rear-side laser patterning at high energy densities, focusing on how rear-side p-type region formation affects front-side passivation through laser-induced shock waves, rather than on contact or edge optimization.
The group identified the rear-side silicon nitride (SiNx) layer as the primary source of damage and revealed the underlying picosecond laser–SiNx interaction mechanism, which is described as a non-thermal ablation process driven by ultrafast energy deposition. It is triggered when the laser pulse excites electrons in the SiNx faster than heat can diffuse, causing rapid bond breaking and localized plasma formation. This leads to a sudden, explosive ejection of material rather than gradual melting or evaporation. The rapid expansion generates shock waves that can propagate into the underlying silicon and induce mechanical stress or damage.
The researchers also investigated the relationship between laser-induced shock waves and device architecture using two sample groups: G1 with a backside SiNx layer and G2 without it. After identical laser ablation and wet etching, G1 was found to exhibit distinct stripe-like damage on the front surface, while G2 showed no morphological abnormalities, indicating the critical role of the backside SiNx layer in amplifying shock-wave effects even at relatively low laser fluence.
In paralle, surface analysis reveals periodic high-reflectivity defects in G1 that match simulated shock-wave intensity distributions, whereas G2 remains defect-free. Cross-sectional scanning electron microscopy (SEM) showed complete loss of pyramidal texture in affected G1 regions, leading to collapse of the passivation stack and failure of light-trapping functionality.
The scientists attributed the damage to shock-wave reflection at the backside SiNx interface, which concentrates stress at pyramid tips, generates microcracks, and promotes preferential silicon etching during subsequent wet processing. This ultimately causes structural collapse of the passivation layer.
To mitigate this issue, they tested three front-side textures: standard pyramids (E1), submicron pyramids (E2), and rounded-top pyramids (E3). Further analysis showed that, while E1 suffers severe degradation after laser processing, E2 and E3 significantly improve passivation stability by reducing stress concentration, with electrical measurements confirming this trend. Photoluminescence imaging further validates improved uniformity for E2 and E3 compared to E1.
The champion solar cell among all devices tested by the team achieved a power conversion efficiency of 27.27%. By way of comparison, the world’s most efficient heterojunction cell developed by Longi itself achieved an efficiency of 28.13%, which means the reported device is only slightly lower in performance and remains very close to the state-of-the-art level.
The result was confirmed by Germany’s Institute for Solar Energy Research Hamelin (ISFH). The cell also achieved an open-circuit voltage of 745.0 mV, a short-circuit current 7,439 mA, and a fill factor of 86.19%.
“We engineered a novel front-side texture consisting of submicron, rounded-top pyramids that effectively disperse stress waves and preserve passivation quality,” concluded Li. “By strategically harnessing shock waves on the rear while mitigating their impact on the front, we achieved improved device stability and performance.”
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