Fig. 1: Suppression of Sn²⁺ oxidation with RbAC.

a FTIR spectra of RbAC and RbAC-SnI₂. XPS spectra of b Sn 3d from the control and target perovskite films. c, d Sn 3d XPS of control and target perovskite films. e, f The contact angle measurement of a water droplet on control and target perovskite films.