A time‐dependent density functional study on optical response in all‐inorganic lead‐halide perovskite nanostructures

Abstract

Recently, all-inorganic perovskite nanostructures have become a hot research topic due to their unique optical response and novel properties. Here, we theoretically study the optical response in Cs 2 PbX 4 and CsPb 2 X 5 (X = Cl, Br, and I) nanostructures.First, to study the ground state, we calculate the band structures of the periodic system using the HSE06 method, which shows that all those periodic perovskites possess the direct band gaps, with distribution from 2.225 to 3.536 eV. Their valence band maximum are mainly contributed from both halogen and lead atoms, while the conduction band minimum are mainly contributed from lead atoms. Then, we study the excited state using the time-dependent density functional theory method and find that, with the increase of halogen atom radius, the photogenerated carrier concentrations in perovskite nanostructures become larger, while the surface plasmon resonance becomes localized rather than long-range. Moreover, through the analysis of photocurrent and local field enhancement, Cs 2 PbX 4 and CsPb 2 X 5 nanostructures exhibit nearly 40 μA photocurrent along the direction of optical polarization. Besides, by regulating the different anions, we predict that field enhancement in Cs 2 PbI 4 and CsPb 2 I 5 share a much stronger distribution at both the center and border parts of Pb-I planes due to localized plasmon resonance, while other perovskites are distributed at the edge parts of Pb-I planes, caused by long-range plasmon resonance. Our research shows that all-inorganic perovskite nanostructures are great candidate materials for developing optoelectronic devices working in high-frequency and high-energy regions and improving their application in sensitive detection and sensors.

Synthesis of Two-Dimensional CsPb2X5 (X = Br and I) with a Stable Structure and Tunable Bandgap by CsPbX3 Phase Separation

“…The bandgaps of CsPb 2 I 5 at different pressures were determined by extrapolating the linear portion of α 2 versus the h ν curve in Tauc plots (inset of Figure b), where α is the absorption coefficient and h ν is the photon energy. The recovered sample exhibits a steep absorbance at 520 nm with a corresponding optical bandgap of 2.38 eV, consistent with the calculated bandgap (2.22 eV) of CsPb 2 I 5 in the theoretical study . It should be noted that the bandgap of CsI is ∼5 eV, far beyond that of CsPb 2 I 5 .…”

“…The recovered sample exhibits a steep absorbance at 520 nm with a corresponding optical bandgap of 2.38 eV, consistent with the calculated bandgap (2.22 eV) of CsPb 2 I 5 in the theoretical study. 49 It should be noted that the bandgap of CsI is ∼5 eV, 46 far beyond that of CsPb 2 I 5 . This means that the occurrence of CsI in the sample did not affect the absorption behavior of CsPb 2 I 5 (Figures S9 and S10 of the Supporting Information).…”

Structural Phase Transitions and Quantum Dots Regulation of Perovskite Stannates

“…The corresponding enthalpies of stable and metastable structures versus pressure are presented in the Supporting Information (Figure S1). Subsequently, the optical properties of ASnO 3 -based QDs were evaluated by employing time-dependent density functional theory (TDDFT) with the usage of the real-space and real-time TDDFT code OCTOPUS, which is an efficient approach to demonstrate absorption spectrum properties. , The Hartwigsen–Goedecker–Hutter (HGH) pseudopotential and the GGA-PBE scheme were employed. The time-dependent Kohn–Sham equations are where ∇ 2 /2, V KS ( r , t ), V ext ( r , t ), V Hatree ( r , t ), and V XC ( r , t ) represent the kinetic energy, Kohn–Sham potential, potential of external fields, electron interactions, and exchange-correlation potential, respectively.…”

“…Subsequently, the optical properties of ASnO 3based QDs were evaluated by employing time-dependent density functional theory (TDDFT) with the usage of the realspace and real-time TDDFT code OCTOPUS, 31 which is an efficient approach to demonstrate absorption spectrum properties. 23,32 The Hartwigsen−Goedecker−Hutter (HGH) pseudopotential and the GGA-PBE scheme were employed. The time-dependent Kohn−Sham equations are…”

Ternary System CsI–PbI2–BiI3 and Thermodynamic Stability of Cesium Metal Halide Perovskites

“…As a sidenote, the Cs 2 PbX 4 and CsPb 2 X 5 compounds, which were studied using time-dependent density functional theory (TD-DFT), do not exist as bulk compounds for X = I, though there can be two-dimensional materials formed via nonambient pressure routes …”