Colloidal Synthesis and Photophysics of M3Sb2I9 (M=Cs and Rb) Nanocrystals: Lead‐Free Perovskites

Herein we report the colloidal synthesis of Cs₃Sb₂I₉ and Rb₃Sb₂I₉ perovskite nanocrystals, and explore their potential for optoelectronic applications. Different morphologies, such as nanoplatelets and nanorods of Cs₃Sb₂I₉, and spherical Rb₃Sb₂I₉ nanocrystals were prepared. All these samples show band‐edge emissions in the yellow–red region. Exciton many‐body interactions studied by femtosecond transient absorption spectroscopy of Cs₃Sb₂I₉ nanorods reveals characteristic second‐derivative‐type spectral features, suggesting red‐shifted excitons by as much as 79 meV. A high absorption cross‐section of ca. 10^?15 cm² was estimated. The results suggest that colloidal Cs₃Sb₂I₉ and Rb₃Sb₂I₉ nanocrystals are potential candidates for optical and optoelectronic applications in the visible region, though a better control of defect chemistry is required for efficient applications.