Correlative and <i>In Situ</i> Microscopy Investigation of Phase Transformation, Crystal Growth, and Degradation of Antimony Sulfide Thin Films

Antimony sulfide (Sb₂S₃), a compound of earth-abundant elements with a highly anisotropic, quasi-layered crystal structure, has triggered growing interest as a solar absorber in photovoltaics and as a phase-change material in memory devices. However, challenges remain in achieving high-quality thin films with controlled nucleation and growth for optimal performance. Here, we investigate the phase transformation, crystal structure and properties, as well as the growth and degradation of atomic layer-deposited Sb₂S₃ thin films using <i>in situ</i> TEM and correlative <i>ex situ</i> analysis. The as-deposited amorphous films crystallized at 243 °C, forming grains with an [100] out-of-plane texture that developed into tens to hundreds of micrometer-long, leaf-shaped grains. Introducing an ultrathin ZnS interfacial layer increased nucleation density, resulting in few-micrometer-sized, more uniform grains while retaining the overall [100] texture. <i>In situ</i> observations and subsequent crystal orientation analysis with cutting-edge 4D-STEM and EBSD revealed that the grains grew faster along the [010] ribbon direction and that the bare films underwent early-stage degradation, forming holes in amorphous regions during annealing. The ZnS interlayer mitigated degradation, stabilizing the films and improving their uniformity. These findings offer valuable insights for optimizing Sb₂S₃ thin films for applications as both solar cell materials and phase-change materials.