Colloidal Synthesis and Photophysics of M₃ Sb₂ I₉ (M=Cs and Rb) Nanocrystals: Lead-Free Perovskites

Herein we report the colloidal synthesis of Cs₃ Sb₂ I₉ and Rb₃ Sb₂ I₉ perovskite nanocrystals, and explore their potential for optoelectronic applications. Different morphologies, such as nanoplatelets and nanorods of Cs₃ Sb₂ I₉ , and spherical Rb₃ Sb₂ I₉ 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 Cs₃ Sb₂ I₉ 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 Cs₃ Sb₂ I₉ and Rb₃ Sb₂ I₉ 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.