No abstract

The structural and electronic properties of both Br substitution and vacancy structures of black orthorhombic CsPbI3 (γ‐CsPbI3) perovskite are investigated by carrying out first‐principle calculations in density functional theory (DFT). For mixed perovskites CsPb(I1−x Br x )3, x is 0.0, 0.25, 0.5, 0.75, and 1.0, respectively. The studies suggest that the III site should be preferentially substituted by Br atom rather than the II site and the structure becomes more stable with increasing Br content. These compounds are direct‐bandgap semiconductors in the range of 1.887−2.137 eV. Moreover, the vacancy changes the electroconductibility of γ‐CsPbI3. γ‐CsPbI3:VPb and γ‐CsPbI3:VI exhibit p‐type and n‐type conductivity, respectively. γ‐CsPbI3:VCs still is a semiconductor with a direct bandgap, which presents a slight decrease in electroconductibility due to the increase in bandgap. The calculated structural parameters show that both substitution and vacancy can induce structural distortion. Partial density of states (PDOS) suggests that the top of the valence band arises from hybridization of Pb s‐ and halogen p‐orbitals, whereas the bottom of the conduction band has predominantly Pb p‐orbitals for two kinds of crystal structures. These results provide strong support for developing high‐performance perovskite photovoltaic materials in optoelectronic devices.

No abstract

The Cs2SnX4 (X = Cl, Br, and I) halide perovskites are currently emerging as a new family of 2D materials and promising candidates for photovoltaic and optoelectronic devices. Herein, the structural, electronic, and optical properties of the Cs2SnX4 multilayers (Ms) with 1–3 layers are investigated by density functional theory (DFT). The structural properties show that the bond length variation of Cs2SnX4 is closely related to surface effects. The Cs2SnCl4 Ms have the lowest formation energies and the best stability, and the formation energies decrease and the stability improves when the number of layers increases. The electronic properties show that the direct‐bandgap semiconductor Cs2SnX4 Ms bandgap values (Cl: 1.513–1.188–0.932, Br: 1.342–1.015–0.862, I: 1.198–0.903–0.729) decrease with the change from 1 to 3 layers and from Cl to I. The p orbitals of X atoms and 5p orbitals of Sn atoms are mainly involved in conduction. The optical properties indicate that Cs2SnX4 Ms achieve coverage and adjustability in the near‐infrared and visible‐light ranges. The calculations provide a fundamental theoretical basis for the research and application of Cs2SnX4.

No abstract