3D micro-photoelectrical mapping reveals hidden subsurface damage at silicon solar-cell edges—and how to passivate it for higher module efficiency 2) Summary Text: Summary, a brief overview of the News

Half-cut architectures are widely used in crystalline silicon (c-Si) photovoltaics because splitting a cell into two smaller pieces can reduce current losses at the module level. However, the same cutting step also creates an extended wafer edge—an area that can accumulate defects and act as a strong recombination site for photogenerated carriers. For manufacturers, a persistent challenge is that many standard electrical tests provide only averaged information, making it difficult to pinpoint how much performance loss comes from the surface versus damage hidden beneath the surface near the cut edge.

In a peer-reviewed study published in Nano Research (Open Access), a team of material scientists led by Baoquan Sun from Soochow University (Institute of Functional Nano & Soft Materials, FUNSOM) and industrial partners report a three-dimensional, spatially resolved micro-photoelectrical mapping method that makes edge losses visible in both space and depth. The approach combines high-resolution photocurrent/photovoltage scanning with multi-wavelength laser excitation to achieve depth sensitivity. By selecting different laser wavelengths, the team can tune how deeply the light probes into c-Si—approximately 0.12 μm, 1.3 μm, and 3.3 μm for 405 nm, 532 nm, and 633 nm excitation, respectively—allowing the reconstruction of how recombination evolves from the surface into the subsurface region along the cut edge.

The team applied the method to industrial n-type tunnel oxide passivated contact (TOPCon) solar cells, which are widely used for high-efficiency silicon photovoltaics. The cells were cut by thermal-laser separation (TLS), a common half-cell manufacturing process. The researchers compared three cases: uncoated cut edges, spatial atomic layer deposition (ALD) of aluminum oxide (AlO_x) for edge passivation, and sequential ALD AlO_x edge passivation. The 3D maps revealed a pronounced photovoltage “valley” near the cut edge, indicating severe carrier recombination triggered by cutting. Crucially, the depth-resolved images showed that TLS can generate not only surface damage but also subsurface and deeper defect states extending several micrometers into the wafer—defects that are difficult to characterize with conventional, surface-weighted techniques.

When the team compared passivation routes, sequential ALD AlO_x consistently suppressed the subsurface recombination signature more effectively than spatial ALD. The improvement also translated into module-level performance. In full-size photovoltaic modules (2278 mm × 1134 mm), the optimized edge passivation increased power conversion efficiency from 22.95% for uncoated modules to 23.17% for modules using sequential ALD AlO_x edge passivation—an absolute improvement of 0.22%. Spectral response evidence further supports that the gain is linked to reduced edge recombination rather than purely optical effects.

“Our aim was to turn edge losses into something you can measure and optimize in three dimensions, instead of treating the cell edge as a single averaged number,” said Prof. Baoquan Sun, a corresponding author of the study. “Depth-sensitive micro-mapping helps us pinpoint where recombination occurs beneath the cut edge—and evaluate how different passivation routes address those hidden defects.”

The researchers also investigated why the two ALD approaches behave differently. Their analysis supports a mechanism in which sequential ALD enables stronger “internal” passivation effects, including enhanced hydrogen-related defect passivation and stronger field-effect passivation associated with fixed charge at the AlO_x/Si interface. In contrast, spatial ALD—while attractive for high-throughput manufacturing—may require additional process engineering or post-treatments to more effectively mitigate deeper defect states beneath the silicon edge.

Looking ahead, the authors say the mapping method could serve as a practical tool for process optimization in silicon PV manufacturing. By linking depth-resolved edge recombination signatures to specific passivation conditions, manufacturers may be able to refine ALD recipes and edge treatments to further reduce edge-related losses in next-generation high-efficiency silicon solar modules.

Other contributors include Tianyu Lan, Jiangtao Li, Yusheng Wang from the State Key Laboratory of Bioinspired Interfacial Materials Science, Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University and Jingsheng Jin, Wei Cui, Jie Yang, Xinyu Zhang from Research and Development (R&D) Department, Zhejiang Jinko Solar Co., Ltd, Haining.

This work is granted by the National Key Research and Development Program of China (2023YFB4202600).

DOI Link:

https://doi.org/10.26599/NR.2026.94908354

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 8,000 articles. In 2025 InCites Journal Citation Reports, its 2025 IF is 9.4 (8.3, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.