Abstract A well-known but heretofore uncharacterized failure mechanism in multijunction photovoltaic cells involves the development of cracks in the top cell directly adjacent to metal gridline structures. In this study, we systematically explore the potential evolution of stress, grain size, roughness, and hardness of metal gridlines during thermal cycling as it pertains to top cell cracking behavior. We discover that although top cells are found to crack after many cycles, this is not due to an accumulation of stress or damage, but rather a progression of strain hardening within the metal gridlines due to cyclic plastic deformations, quantified as an increase in hardness of as much as 57%. Furthermore, optical and topological characterization reveals morphology changes at the gridlines’ top surfaces, lending some insight to commonly observed bus bar wire-bonding issues. Ultimately this suite of characterization techniques not only reveals the underlying behavior leading to gridline-induced top cell cracking failures in multijunction photovoltaics, but also suggests a route forward for the development of improved gridline materials.

中文翻译：

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热循环引起的多结光伏网格线退化

摘要 多结光伏电池中众所周知但迄今为止未表征的失效机制涉及直接与金属网格线结构相邻的顶部电池中裂纹的发展。在这项研究中，我们系统地探索了热循环过程中金属网格线的应力、晶粒尺寸、粗糙度和硬度的潜在演变，因为它与顶部电池开裂行为有关。我们发现，虽然在多次循环后发现顶部电池破裂，但这不是由于应力或损坏的积累，而是由于循环塑性变形导致金属网格线内应变硬化的进展，量化为硬度的增加高达 57%。此外，光学和拓扑表征揭示了网格线顶面的形态变化，对常见的汇流条引线键合问题提供一些见解。最终，这套表征技术不仅揭示了导致多结光伏电池中由网格线引起的顶部电池开裂故障的潜在行为，而且还为开发改进的网格线材料提供了一条前进的道路。