Contactless plating with electroless solutions can provide self-aligned high-efficiency contacts with very low silver content, using simple and inexpensive equipment. With prior surface activation, it can even be used to metallize both sides of bifacial silicon solar cells simultaneously. However, we observe in such a coplating process with nickel, where surface activation is achieved by immersion plating and thickening by electroless plating, that V _oc and fill factor can sometimes significantly decrease with immersion-plating time. To understand the reason for this electrical degradation, we studied the impact of immersion plating on the microstructure of the plated silicon surface. The evolution of the Si-Ni interface was studied by scanning and transmission electron microscopies, energy-dispersive X-ray analysis, secondary ion mass spectrometry, and scanning spreading resistance microscopy. Our attention focused on metal in-diffusion, silicon roughening and etching as the origin for increased recombination. Etching was found to have a significant impact on V _oc . The thickness of N ⁺ Si etched during Ni deposition can in fact suppress in a few locations most of the field-effect passivation underneath the contacts. This means that a thicker surface field with doping beyond 10 ¹⁹ /cm ³ must be foreseen under the plated areas, or that the amount of Si lost in the reaction must be reduced. Our observations also confirm that immersion plating can hinder silicide formation and allow Ni in-diffusion, which may be a concern for reliability.

中文翻译：

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了解双面太阳能电池共镀后复合损失的起源：深入的微观结构研究

使用化学镀溶液进行非接触电镀可以使用简单且廉价的设备提供具有极低银含量的自对准高效触点。通过预先表面活化，它甚至可以用于同时对双面硅太阳能电池的两侧进行金属化。然而，我们观察到在这种与镍的镀覆工艺中，通过浸镀和化学镀增厚实现表面活化，即伏 _oc和填充因子有时会随着浸镀时间的增加而显着降低。为了了解这种电退化的原因，我们研究了浸镀对镀硅表面微观结构的影响。通过扫描和透射电子显微镜、能量色散 X 射线分析、二次离子质谱和扫描扩散电阻显微镜研究了 Si-Ni 界面的演变。我们的注意力集中在金属扩散、硅粗糙化和蚀刻作为增加复合的起源。发现蚀刻对伏 _奥 。厚度N ⁺在 Ni 沉积过程中蚀刻的 Si 实际上可以在几个位置抑制触点下方的大部分场效应钝化。这意味着必须预见在电镀区域下掺杂超过 10 ¹⁹ /cm ³的更厚表面场 ，或者必须减少反应中损失的硅量。我们的观察还证实，浸镀会阻碍硅化物的形成并允许 Ni 扩散，这可能是可靠性的一个问题。