Compositional Modulation of Two-Dimensional Layered Perovskite (RNH₃)₂Pb(Cl, Br, I)₄ and Its Optical Properties

Abstract

The compositional modulation of two-dimensional layered perovskites, (RNH 3 ) 2 Pb(X, I) 4 (R: C 6 H 5 C 2 H 4 -; X: Cl, Br), and optical properties of these materials were investigated. Thin films of microcrystalline (RNH 3 ) 2 - Pb(X, I) 4 were successfully fabricated by the spin-coating method. X-ray diffraction spectra revealed that these materials could be regarded as inorganic/organic superlattice structures. In the spectra obtained for the (RNH 3 ) 2 Pb(Br, I) 4 films, a strong exciton absorption band was observed even at room temperature, and the peak position shifted continuously towards the blue and violet regions. The exciton absorption bands observed in the spectrum of (RNH 3 ) 2 Pb(X, I) 4 mixed crystal were consistent with the 6s to 6p transition of Pb 2+ . The peak shift of the exciton absorption bands of these materials could be explained by the valence band structure composed of the Pb(6s) orbital which was hybridized with the I(5p) and X(np) orbitals.