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Despite their clear efficiency advantages, high-resistivity, lightly doped silicon wafers have seen limited adoption in commercial solar cell production.
Despite their clear efficiency advantages, high-resistivity, lightly doped silicon wafers have seen limited adoption in commercial solar cell production. These wafers offer fewer recombination sites, which can significantly enhance electrical performance, but their practical use has been hindered by fragility. 
They are more prone to cracking during handling, sawing, or module assembly, making them challenging for large-scale manufacturing. By comparison, standard Czochralski-grown silicon wafers, with moderate to low resistivity, dominate the mass-market PV sector. 
Their mechanical robustness and tolerance to thermal and mechanical stress make them easier to process and far less likely to suffer damage during production. This reliability comes at the cost of slightly lower theoretical efficiency, yet it remains a key reason these wafers continue to be the industry standard.
To close the efficiency gap, Chinese manufacturer Longi, together with researchers from Sun Yat-sen University, explored using edge passivation to strengthen high-resistivity wafers while preserving high efficiency and fill factor, pv magazine writes.
Early experiments showed that high-resistivity wafers often underperform compared to standard wafers. The study found that these wafers operate at higher excess carrier densities at the maximum power point and have flatter concentration gradients, which reduces carrier collection and in turn makes them highly sensitive to edge recombination. Without proper passivation, the wafer edges act as a drain, negating the theoretical performance benefits these wafers could provide.
Furthermore, the team demonstrated that pairing high-resistivity wafers with in-situ edge passivation is essential to manage their sensitivity and unlock their full performance. High-resistivity wafers enter the high-level injection regime more readily than low-resistivity ones, a physical characteristic that underlies their superior intrinsic potential for achieving high fill factors. 
By controlling edge recombination through passivation, these wafers can maintain strong carrier collection and high efficiency, translating their theoretical advantages into practical, high-performing solar cells.
The team fabricated hybrid interdigitated back-contact (HIBC) solar cells measuring 7.2 in × 3.6 in using either high-resistivity or standard Czochralski-grown wafers. The main difference was that the edges of high-resistivity wafers were left without silicon nitride during chemical vapor deposition, leaving the SiOx/n-poly-Si passivation layer unprotected and partially removed during wet chemical cleaning.
The full production process included wet chemical cleaning, chemical vapor deposition (CVD), phosphorus diffusion, atomic layer deposition (ALD), laser patterning, physical vapor deposition (PVD), isolation, and screen printing. High-resistivity wafers had resistivity values of 8–10 Ω·cm (0.046–0.058 Ω·in), while standard wafers measured 1.0–1.5 Ω·cm (0.006–0.009 Ω·in). This setup allowed the team to directly compare performance and show how edge passivation affects high-resistivity wafer behavior.
The team evaluated both cell types using an I-V tester, wafer metrology system, transmission electron microscopy, and simulation software. Their analysis showed that adding effective edge passivation improved performance in both low- and high-resistivity solar cells, though the gains were larger for high-resistivity wafers. For low-resistivity cells, edge passivation increased the pseudo-fill factor by 0.48% and efficiency by 0.34%, demonstrating that controlling edge recombination enhances overall device performance even in wafers with moderate resistivity.
Bojan Stojkovski is a freelance journalist based in Skopje, North Macedonia, covering foreign policy and technology for more than a decade. His work has appeared in Foreign Policy, ZDNet, and Nature.
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