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Exploring the conduction mechanism in the chalcogenide perovskite Ba Zr S 3 is of significant interest due to its potential suitability as a top absorber layer in silicon-based tandem solar cells and other optoelectronic applications. Theoretical and experimental studies anticipate native ambipolar doping in Ba Zr S 3 , although experimental validation remains limited. This study reveals a transition from highly insulating behavior to n -type conductivity (approximately 100 S/cm) in Ba Zr S 3 thin films through annealing in an S -poor environment. Ba Zr S 3 thin films are synthesized via a two-step process: co-sputtering of Ba - Zr followed by sulfurization at 600 ∘ C , and subsequent annealing in high vacuum. Ultraviolet-visible spectroscopy measurements reveal a red shift of approximately 100 meV in the band gap concurrent with sample-color darkening after vacuum annealing. The increase in defect density from the order of 10 17 to 10 21 cm − 3 with vacuum annealing, coupled with the low activation energy (approximately 8 meV), and the n -type character of the defects, strongly suggests that sulfur vacancies ( V S ) are responsible for the n -type doping, in agreement with theoretical predictions. Temperature-dependent Hall measurement shows that phonon scattering governs charge transport at room temperature in Ba Zr S 3 films and that S vacancies are shallow donor defects acting as a weak impurity metal. The shift of the valence-band maximum (VBM) with respect to the Fermi level, quantified by hard x-ray photoelectron spectroscopy ( Ga K α , 9.25 keV), further corroborates the induced n type of conductivity in annealed samples. Our findings indicate that vacuum annealing induces V S defects that dominate charge transport, resulting in n -type conductivity in Ba
Aggarwal et al. (Tue,) studied this question.