A Raman Scattering Investigation of Halide Rb₄Ag₂BiBr₆

Halide perovskites have reached photovoltaic efficiencies near the theoretical maximum but due to toxicity and stability issues other alternatives have been sought out. The double perovskite structure has been found to address these issues however the strong exciton-phonon coupling reduces carrier transport increasing electron-hole recombination rates[1]. Rb₄Ag₂BiBr₆ has been proposed as an alternative structure type to the halide double perovskites. The crystal structure is similar to that of

double perovskite Cs₂AgBiBr₆ which consists of alternating BiBr₆ octahedral groups surrounding a central cation, with Rb₄Ag₂BiBr₆ containing additional AgBr₅ square pyramids. Using a controlled cooling synthesis technique[2] Rb₄Ag₂BiBr₆ crystals have been successfully synthesized. The composition has been confirmed via X-ray powder diffraction and Energy Dispersive X-ray spectroscopy. Temperature and polarization dependent Raman scattering spectroscopy measurements will be presented to analyze the vibrational modes.

[1] C.N. Savory et al. ACS Energy Letters. 1 (5), 949−955, 2016.

[2] L. Yin et al. Advanced Optical Materials. 7 (19) 1900491, 2019.