Enhancing the optical absorption of chalcogenide perovskite BaZrS3 by optimizing the synthesis and post-processing conditions

Recently, chalcogenide perovskite BaZrS3 has been proposed as one of the most promising absorption materials due to its high absorption and excellent carrier transport properties comparable with lead-halide perovskites, as well as its good stability. However, the dependence of light absorption abilities on the synthesis and post-processing conditions of BaZrS3 is still ambiguous. In this work，an improved sulfurization experimental technique was introduced and the conversion rate was proposed as an indicator of the sulfurization level. Then, a series of barium zirconium oxysulfide powders were prepared to investigate the influences of sulfurization level on their structural and absorption properties. Besides, the thermal stability, structures and absorption spectra of BaZrS3 under different post-annealing conditions were compared and discussed. The stronger light absorption was observed under moderate rather than fully sulfurized samples. The structures of BaZrS3 remained unchanged even at temperatures as high as 400 ​°C in the air or even 700 ​°C at low pressure of 10−1 ​Pa. Post-annealing in the air was helpful to improve the absorbance of BaZrS3, probably by introducing oxide related states in the band gap. In summary, oxide impurities that inevitably and commonly exist in BaZrS3 may not be a serious issue, but can be helpful to get a higher absorbance. The above findings confirm the effectiveness of sulfurization strategy to enhance the light absorption ability of BaZrS3, highlighting the promising prospects of such stable and non-toxic chalcogenide perovskite into practical photovoltaic devices. An improved equipment was designed to sulfurize BaZrO3 oxide precursors into chalcogenide perovskite BaZrS3 without involving the carrier gas, and the conversion rate was proposed as an indicator for the sulfurization level. It is found that higher absorption can be reached even in incompletely sulfurized samples or by optimizing the post-processing conditions, indicating the potential of chalcogenide perovskite BaZrS3 as highly stable light absorption materials. [Display omitted] •An improved sulfurization technique was introduced and the conversion rate can indicate the sulfurization level.•The stronger light absorption was observed under moderate rather than fully sulfurized samples.•The structures of BaZrS3 remained unchanged even at high temperatures of 700 ​°C at low pressure of 10−1 ​Pa.•Oxide impurities that inevitably and commonly exist in BaZrS3 can b