In the present work, the substitution of cesium (Cs + ) with rubidium (Rb + ) in fully inorganic tin bromide perovskites Cs 1-x Rb x SnBr 3 , has been experimentally demonstrated by synthesizing pure single-phase samples in the CsSnBr 3 -Cs 0.70 Rb 0.30 SnBr 3 compositional range. The substitution of Cs with Rb is responsible for structural modification from cubic to orthorhombic symmetry, which has been correlated with optical properties, as the band gap varies from 1.719 to 1.817 eV from CsSnBr 3 to Cs 0.70 Rb 0.30 SnBr 3 sample. Notably, all of the rubidium-embedding alloys present good air stability. All of these results are very straightforward and open the possibility to exploit the electrical and optical capabilities of this very promising family of lead-free materials. © Copyright 2019 American Chemical Society.