Synthesis of BaZrS₃ Perovskite Thin Films via Different Solid BaS _x Intermediate Phases

The BaZrS₃ perovskite has emerged as a promising compound for photovoltaic (PV) applications due to its unique optoelectronic properties, stability, and abundance of the constituent elements. Recent research has devoted considerable effort to decreasing the processing temperature to facilitate the integration of BaZrS₃ thin films into optoelectronic devices. In this context, the formation of a barium polysulfide liquid flux as an intermediate phase is anticipated to promote BaZrS₃ synthesis. This study investigates whether solid binaries can also accelerate the process at lower temperatures, i.e., below melting. To address this question, Ba-Zr precursors were sulfurized under various conditions that favor the formation of distinct solid BaS _x intermediate phases during BaZrS₃ synthesis, achieved by deliberately selecting processing temperatures below the melting points of any of the involved binary sulfides. The crystallinity of the resulting BaZrS₃ thin films is evaluated by X-ray diffraction and transmission electron microscopy, revealing that the sulfurization conditions that favor solid BaS₃ offer a greater advantage for BaZrS₃ formation than those that promote BaS₂, which in turn prove more favorable than those that favor BaS. Moreover, by varying sulfur partial pressure and sample temperature during sulfurization, this study disentangles the effects of these two parameters on BaZrS₃ crystallization: the results indicate that the sulfurization conditions that favor BaS₃ effectively promote BaZrS₃ nucleation, while high temperatures predominantly enhance grain growth.