First-Principles Investigation of Optoelectronic Structure and Thermodynamic Properties of Ruddlesden-Popper Halide Perovskites for Optoelectronic Applications

The structure optimization, nuclear magnetic resonance (NMR) shielding, optoelectronic and thermodynamic properties of 2D layered Ruddlesden-Popper halide perovskites (RP-HPs) Cs₂CdX₄ (X = Cl, Br, I) are computed using first-principles simulations. The crystal structure is composed of 2D [CdX₄]_n²ⁿ⁻plane constructed by CdX₆ octahedral vertices and inorganic spacer cation (Cs⁺) separates the octahedral layers. At the valence band (VB) edge, X-p and Cd-p orbitals are strongly hybridized, which play a key role in the optoelectronic applications of these compounds owing to the excitation of their valence electrons to the conduction band (CB) with minimum photon’s energy. The pseudo-direct and tunable band gaps of the understudy 2D layered RP-HPs are well-suited for optoelectronic applications. The numerical values of Debye temperature illustrates that each compound excites with different Debye frequency, corresponds to the unit cell size and phonon’s wavelength. The specific heat capacity curves are consistent with equipartition theorem of classical mechanics and obey the Dulong-Petit law at high temperature. The positive entropy change (ΔS) spirits negative change in Gibb’s free energy (ΔG), confirming the stability of these materials. The isotropic chemical shift depends on Cd and halides coordinates therefore, Cd-δ_iso is decreases and X-δ_iso increases with the halide increments. The Cs-p, Cd-d, and X-s orbital play a key role in NMR shielding owing to their existence in lower VB.