The interface of high-quality crystalline silicon/hydrogenated amorphous silicon (c-Si/a-Si:H) is indispensable for achieving the ideal conversion efficiency of Si heterojunction solar cells. Therefore, it is extremely desirable to characterize and control the interface at the atomic scale. Here, we employ spherical aberration-corrected transmission electron microscopy to investigate the atomic structure of the c-Si/a-Si:H interface in high-efficiency Si heterojunction solar cells. Their structural evolution during in situ annealing is visualized at the atomic scale. High-density embedded nanotwins, detrimental to the device performance, are identified in the thin epitaxial layer between c-Si and a-Si:H. The nucleation and formation of these nanotwins are revealed via ex situ and in situ high-resolution transmission electron microscopy. Si heterojunction solar cells with low-density nanotwins are fabricated by introducing an ultra-thin intrinsic a-Si:H buffer layer and show better performance, indicating that the strategy to restrain embedded nanotwins can further enhance the conversion efficiency of Si heterojunction solar cells.

高质量的晶体硅/氢化非晶硅（c-Si/a-Si:H）的界面对于实现Si异质结太阳能电池的理想转换效率是必不可少的。因此，在原子尺度上表征和控制界面是非常可取的。在这里，我们使用球差校正透射电子显微镜来研究高效硅异质结太阳能电池中 c-Si/a-Si:H 界面的原子结构。它们在原位退火期间的结构演变在原子尺度上可视化。在 c-Si 和 a-Si:H 之间的薄外延层中发现了对器件性能有害的高密度嵌入式纳米孪晶。通过异位和原位高分辨率透射电子显微镜揭示了这些纳米孪晶的成核和形成。