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.