Investigation of chalcogenide perovskite BaZrS3 thin films from oxide precursors

BaZrS3 is a chalcogenide perovskite composed of earth-abundant elements with potential applications for photovoltaic (PV) energy conversion. While it is a promising candidate, many of its properties remain unexplored as of yet. For applications, a comprehensive understanding of the material properties is necessary. To accelerate the research, the combinatorial approach was chosen, involving compositional gradients and high throughput experimentation. BaZrS3 thin lms with a compositional gradient from Zr-rich to Ba-rich were produced from oxide precursors using pulsed laser deposition with subsequent sulfurization in H2S gas. Temperature and H2S concentration variation series enable the study of the evolution of di erent structural and optoelectronic properties with processing conditions. Using mapping techniques for investigating those properties as a function of the elemental composition, it was possible to develop a model for the growth of BaZrS3 as well as a model for point defects in BaZrS3. A phase diagram of Ba-Zr-S-O was constructed from the investigation of the thin films with grazing incidence X-ray diffraction. In combination with the grain sizes observed in scanning electron microscopy images, it was possible to describe the growth process of BaZrS3. The results show that sulfurization of the oxide precursor occurs more readily in the presence of BaS, which is more commonly found for Ba-rich compositions. This was not indicative of BaZrS3 formation however, as RuddlesdenPopper phase formation is more prevalent under Ba-rich conditions if not enough sulfur has not been incorporated yet. In addition, it was found that BaZrS3 can only incorporate a limited amount of excess barium or zirconium. Excess of those elements leads to formation of secondary phases, such as the aforementioned RuddlesdenPopper phases for Ba-excess or ZrO2 for Zr excess. By means of absorption spectroscopy measurements, band gap variations between 1.88-1.97eV were found for compositions close to the stoichiometric point in libraries synthesized at 1000◦C. While these band gap energies remain constant between [Ba]/([Ba]+[Zr]) = 0.47-0.51, further o-stoichiometry yields a slight increase in band gap energy for Zr-excess and a sharp increase for Ba-excess. The investigation of the optoelectronic properties of BaZrS3 suggests a high defect density of both donors and acceptors in BaZrS3 synthesized in this way. These defects impact optoelectronic properties, increasing sub band gap absorption. In addition to shallow donor and acceptor levels related to point defects, such as VS and Si, the analysis of low temperature photoluminescence revealed several deep defect states in the band gap, associated with point defects like Si and BaZr.