Ramifications of co-substitution on crystal structure and optical performance of RT synthesized Cs1-xPbI3-x - xRbCl (x=0 to 0.8) solid solutions

Abstract

δ-CsPbI₃, a stable yellow-colored and orthorhombic polymorph of CsPbI_3, has been subjected to compositional engineering by incorporating stoichiometric amounts of RbCl via mechanochemical synthesis method. Such developed compositions Cs_1-xPbI_3-x-xRbCl that facilitates both cation/anion exchange, have been explored for their in-depth structural modification and optical properties. The bond distances were obtained through Rietveld refinement of the high-resolution X-ray diffraction data. The distortion index calculated for the Pb–I octahedra increased from 0.017 for x = 0 to 0.021 for x = 0.8 indicating stronger distortion in the lattice with RbCl incorporation. Absorption wavelength of the compositions shifted to lower wavelengths with increase in x. Resultantly, band gap calculated (E_g) also increased from 2.41 eV to 2.73 eV with increase in x – which affirms the narrowing of bands via small dopants. Photoluminescence studies carried out on the as-synthesized solid solutions showed single emission around 567 nm for x = 0; whereas two emission wavelengths observed around 515 nm and 577 nm (green region) for x = 0.2 to 0.8. Better PL intensities observed exclusively for the RbCl substituted compositions may be attributed to the defect-mediated suppression of non-radiative process. ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠