Structural Characterisation of BaZrS_(3-y)Se_y Perovskite Thin Films via Scanning Transmission Electron Microscopy

Chalcogenide perovskites show great potential for becoming solar cell materials due to their tuneable and direct bandgaps in the visible range, great physical properties compared to oxide perovskites, and use of nontoxic and abundant elements [1]. However, difficulties in growing thin films using chalcogen sources has hindered their progress until recently. Expanding on previous work on one-step synthesis of BaZrS₃ (BZS) thin films via molecular beam epitaxy [2], here we demonstrate the synthesis of a BaZrS_(3-y)Se_y (BZSSe) alloy system using a BZS template layer on LaAlO₃ (LAO).<br/>These BZSSe films are analysed via high resolution scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS). Both the template and the alloy are noted to be of a perovskite structure, with both growth modes as previously seen in pure BZS films, present. While the film is relaxed overall, there is a large concentration of out-of-plane antiphase boundaries (APBs) in the template region; conversely, there is a large concentration of in-plane APBs in the alloy region. EDX and EELS indicate the presence of diffused Se even down to the substrate interface, which correlates with the presence of APBs as a strain relaxation mode.<br/><br/>References:<br/><br/>[1] Jaramillo, R. & Ravichandran, J. In praise and in search of highly-polarizable semiconductors: Technological promise and discovery strategies. <i>APL Mater</i>. 7, 100902 (2019).<br/>[2] Sadeghi, I. <i>et al</i>. Making BaZrS3 Chalcogenide Perovskite Thin Films by Molecular Beam Epitaxy.<i> Adv. Funct. Mater</i>. 31, 2105563 (2021).