Colloidal Synthesis and Photophysics of M 3 Sb 2 I 9 (M=Cs and Rb) Nanocrystals: Lead‐Free Perovskites

Herein we report the colloidal synthesis of Cs 3 Sb 2 I 9 and Rb 3 Sb 2 I 9 perovskite nanocrystals, and explore their potential for optoelectronic applications. Different morphologies, such as nanoplatelets and nanorods of Cs 3 Sb 2 I 9 , and spherical Rb 3 Sb 2 I 9 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 Cs 3 Sb 2 I 9 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  cm 2 was estimated. The results suggest that colloidal Cs 3 Sb 2 I 9 and Rb 3 Sb 2 I 9 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.