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<p>Sn-Bi-based solders used in photovoltaic interconnections are prone to severe oxidation during high-temperature processing, which degrades surface quality and solderability. In this work, Sn-Bi-In alloys containing 1-8 wt.% In were prepared to quantify how In content alters oxidation kinetics and oxide-film development at elevated temperature. Oxidation on the molten surface was monitored in air, and the resulting oxide layers were examined by XRD, SEM, and XPS. The results indicate that In, owing to its higher oxygen affinity than Sn and Bi, is consumed preferentially at the surface and reshapes the oxidation pathway. Increasing In content stabilizes a bright molten surface and suppresses oxide buildup, accompanied by distinct microstructural responses: the high-In alloy (1-10#) forms a refined surface structure with Bi precipitation after oxidation, whereas the low-In alloy (1-12#) exhibits pronounced Bi-phase coarsening. The oxide film is composed mainly of SnO/SnO<sub>2</sub> and In<sub>2</sub>O<sub>3</sub>, and XPS depth profiling reveals In enrichment near the surface that strengthens with increasing In content, consistent with diffusion-driven replenishment during oxidation. Notably, oxide-film thickness decreases from 152&#xa0;nm (low-In) to 77&#xa0;nm (high-In), which is associated with In<sup>3</sup>⁺ incorporation into the SnO lattice and the resulting increase in metal vacancies that reduces electronic transport and limits further oxidation. Overall, In improves oxidation resistance through coupled chemical and electronic effects, providing a practical basis for designing oxidation-tolerant, lead-free photovoltaic solder alloys.</p>

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Indium-Enabled Oxidation Resistance in Sn-Bi-In Solder Alloys at High Temperature: Surface Oxide Evolution and Mechanisms

  • 期刊论文

  • 发表日期：

    2026年7月6日

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  • Jiacheng He,
  • Yilin Zhu,
  • Shanshan Cai,
  • Xiaojing Wang,
  • Mengxia Wei,
  • David P. Yan

摘要

Sn-Bi-based solders used in photovoltaic interconnections are prone to severe oxidation during high-temperature processing, which degrades surface quality and solderability. In this work, Sn-Bi-In alloys containing 1-8 wt.% In were prepared to quantify how In content alters oxidation kinetics and oxide-film development at elevated temperature. Oxidation on the molten surface was monitored in air, and the resulting oxide layers were examined by XRD, SEM, and XPS. The results indicate that In, owing to its higher oxygen affinity than Sn and Bi, is consumed preferentially at the surface and reshapes the oxidation pathway. Increasing In content stabilizes a bright molten surface and suppresses oxide buildup, accompanied by distinct microstructural responses: the high-In alloy (1-10#) forms a refined surface structure with Bi precipitation after oxidation, whereas the low-In alloy (1-12#) exhibits pronounced Bi-phase coarsening. The oxide film is composed mainly of SnO/SnO2 and In2O3, and XPS depth profiling reveals In enrichment near the surface that strengthens with increasing In content, consistent with diffusion-driven replenishment during oxidation. Notably, oxide-film thickness decreases from 152 nm (low-In) to 77 nm (high-In), which is associated with In3⁺ incorporation into the SnO lattice and the resulting increase in metal vacancies that reduces electronic transport and limits further oxidation. Overall, In improves oxidation resistance through coupled chemical and electronic effects, providing a practical basis for designing oxidation-tolerant, lead-free photovoltaic solder alloys.