Fig. 1. Structural and optoelectronic properties modulated by alkali cations.

(A) XRD patterns, (B) the lattice constants, and (C) the FWHM of the perovskite peak. The lattice constants and FWHM were extracted from the peak at around 14°. a.u., arbitrary unit. (D) Steady-state PL spectra. (E) Time-resolved PL decay curves for samples with different cation combinations. Elongation of PL lifetime is observed with the addition of alkali cations.