In situ study of crystal plane-dependent interfacial structural transformation in AgBiS2

The compound AgBiS2, a ternary sulfide, has gained significant attention in the field of photovoltaics due to its characteristic properties of being non-toxic, low-cost, and highly efficient. However, due to the instability of its grain boundaries, the structure of the AgBiS2 may be transformed at high temperatures, consequently influencing the lifetime of devices utilizing this material. In this study, the mechanism of interfacial structural transition and the factors affecting the stability of AgBiS2 were investigated by in-situ transmission electron microscopy. Our observations revealed that, under high-temperature conditions, the structure of the material changes with the formation of triangular hole-like defects at the AgBiS2 interface, which is directly related to the movement of defects. Furthermore, the surface energy of the AgBiS2 crystal planes is different due to different atomic arrangements. Combining the experiments with theoretical calculations, we found that the defects such as dislocations tend to cluster on the high-energy plane (111), thereby leading to localized stress and strain concentration. Then, the structure transforms by reconstructing its interfacial atoms to reduce the local stress. Of note, this reconstruction leads to the formation of triangular hole-like defects, consequently reducing the overall energy of the system.