3月13日，据pv-magazine报道，新南威尔士大学（UNSW）与中国光伏组件制造商隆基的研究团队发现，TOPCon电池背面采用的氮化硅（SiNx）层对钠（Na）污染物的化学降解尤为敏感，可能导致显著的开路电压（Voc）损失并降低电池效率。

该研究团队在《太阳能材料与太阳能电池》（Solar Energy Materials and Solar Cells）期刊发表了题为《缓解TOPCon太阳能电池污染物诱导表面退化：机制、影响与解决方案》的论文。研究表明，背面SiNx层的化学脆弱性可能引发开路电压大幅下降、电阻显著增加及整体性能衰退。

实验中，研究人员通过模拟湿热（DH）环境测试，评估了多种钠盐对23%效率商用TOPCon电池的影响。DH测试是一种加速老化试验，需将光伏组件置于85℃、85%相对湿度的温控箱中至少运行1000小时。测试样本采用硼扩散发射极结构，正面包含多层钝化堆叠（氧化铝AlOx、SiNx层及氮氧化硅SiOyNz减反射涂层），背面则由隧穿氧化硅SiO₂、掺磷多晶硅poly-Si及额外SiNx减反射层构成。正电极采用银铝（Ag/Al）合金化工艺，背面电极通过丝网印刷银浆制备。

结果显示，醋酸钠（CH₃COONa）和氯化钠（NaCl）两种钠污染物对电池性能的损害最为显著：

当背面接触CH₃COONa时，电池效率相对下降16%，开路电压损失达5.8%，且填充因子（FF）严重衰减；

NaCl污染则导致效率相对降低4.8%。

研究指出，钠盐引发的化学反应会加速背面SiNx层氧化、钝化失效，进而影响关键性能参数。为此，团队提出在电池正面引入10纳米原子层沉积（ALD）氧化铝（AlOx）阻隔层，有效抑制污染物扩散。实验表明，该方案在20小时加速DH测试中仅造成微小效率损失（<0.5%），并维持开路电压稳定。此外，AlOx层还能缓解钠盐导致的腐蚀与复合缺陷，验证了其作为TOPCon电池长效保护方案的可行性。

"加速老化测试证实，AlOx层显著降低了退化风险，为工业量产提供了可扩展的解决方案。" 论文通讯作者Bram Hoex表示，"未来我们将优化阻隔层集成工艺，并进一步研究其在真实户外环境下的长期稳定性表现。"

此前，UNSW团队已揭示TOPCon电池易受接触腐蚀及三种独特的衰减效应，而这三种效应没有在PERC电池中出现过。

报道原文如下：

Researchers from UNSW and Longi have found that the silicon nitride layers used in TOPCon cell rear-side are particularly prone to chemical degradation from sodium contaminants. This can lead to significant open-circuit voltage losses and reduce cell efficiency.

A research team from theUniversity of New South Wales (UNSW) and Chinese solar module maker Longi has investigated sodium-induced degradation of TOPCon solar cells under damp-heat exposure and has found that the silicon nitride (SiNx ) layer on the cell rear-side is particularly vulnerable to chemical degradation from sodium (Na) contaminants.

“This topic has not received much attention to date but is a serious concern now that the stability of front metallization has improved,” the research's corresponding author, Bram Hoex, toldpv magazine.

In the paper “Mitigating contaminant-induced surface degradation in TOPCon solar cells: Mechanisms, impacts, and mitigation,” which was recently published inSolar Energy Materials and Solar Cells, Hoex and his colleagues explained that SiNx rear-side vulnerability can lead to significant losses of open-circuit voltage, substantial resistance increase, and overall cell performance degradation.

The researchers used several Na-related salts to investigate open-circuit voltage degradation in TOPCon solar cells under cell-leveldamp-heat (DH) testing. The DH test is an accelerated test that tests the reliability of modules under extreme humidity and heat. In its standard form, the PV is placed in a controlled chamber with a temperature of 85 C and humidity of 85% for at least 1,000 h.

The tests were conducted on commercial types of 23%-efficient TOPCon cells. On the front side, the devices featured a boron-diffused emitter, passivated by a multilayer stack of aluminum oxide (AlOx), a SiNxlayer, and a silicon oxynitride (SiOyNz) layer as an antireflection coating (ARC).

On the rear side, the cells had a tunneling silicon oxide (SiO2) layer, a phosphorus-doped polycrystalline silicon (poly-Si) layer, and an additional SiNxARC layer. Furthermore, the front side was treated with silver (Ag) and aluminum (Al), while the rear-side contact was formed using a screen-printed Ag paste.

The HD testing was conducted for 20 h in an ASLi environmental chamber at 85 C with 85% relative humidity (DH85). It showed that particularly two sodium contaminants – CH3COONa andsodium chloride (NaCl) – were responsible for significant performance losses.

“In our experiments, the application of CH3COONa on the rear side of the TOPCon cells led to a substantial 16% loss in efficiency, while NaCl caused a 4.8% relative decrease,” the academics stated. “The rear-side SiNxlayer was particularly susceptible to chemical reactions and surface degradation when exposed to sodium-based salts, resulting in increased oxidation, passivation loss, and a marked reduction in key performance parameters, such as open-circuit voltage, with severe fill factor (FF) degradation when treated with CH3COONa.”

The analysis also showed that open-circuit voltage losses can reach up to 5.8%, with relative loss in overall cell efficiency being around 16%.

The research group proposed to address the analyzed degradation mechanisms by introducing on the cell front side a 10 nm aluminum oxide (AlOx) barrier layer, deposited via atomic layer deposition (ALD), to protect against contaminant diffusion.

“This layer effectively reduced performance degradation, demonstrating only minor decreases in efficiency and maintaining open-circuit voltage stability after 20 h of accelerated damp-heat testing,” it further explained. “The AlOxlayer also mitigated corrosion and recombination defects induced by sodium-related salts, confirming its potential as a robust protective solution to enhance the long-term reliability of TOPCon solar cells under harsh environmental conditions.”

“Accelerated damp-heat testing confirmed that the AlOx layer significantly reduces degradation, maintaining long-term stability,” Hoex added. “Our solution represents a scalable and industrially viable approach for improving TOPCon solar cell reliability.”

Looking forward, the academics said they want to better integrate barrier layers in commercial production and analyze long-term degradation behaviors under real field conditions.

Previous research by UNSW showed thevulnerability of TOPCon solar cells to contact corrosion and three types of TOPCon solar module failures that were never detected in PERC panels.