Effects of Bromine Substitution and Vacancy Defects on the Structural and Electronic Properties of Black Orthorhombic CsPbI₃ Perovskite

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.

Significant Impact of Defect Fluctuation on Charge Dynamics in CsPbI3: A Study Combining Machine Learning with Quantum Dynamics

“…The Cs element does not participate in the band edge, as evidenced by the charge densities. The CBM and VBM of pristine CsPbI 3 are separated by a wide bandgap of 1.72 eV (Figure a), which aligns closely with the experiment and DFT calculations . The three types of defects studied minimally affect the bandgap but introduce midgap states.…”

“…The CBM and VBM of pristine CsPbI 3 are separated by a wide bandgap of 1.72 eV (Figure 1a), which aligns closely with the experiment 32 and DFT calculations. 33 The three types of defects studied minimally affect the bandgap but introduce midgap states. Specifically, the Cs I defect creates a deep electron trap state 1 eV below the CBM (Figure 1b),whereas the singly occupied I i defect acts as a deep hole trap at 0.3 eV above the VBM (Figure 1d).…”

Low-Trap-Density CsPbX3 Film for High-Efficiency Indoor Photovoltaics

“…A small amount of Br ions that have not entered the crystal lattice will exist in the form of amorphous PbBr 2 , which can also effectively passivate the defects. Meanwhile, it also increases the structural stability and prevents ion migration to suppress the formation of point defects. − Therefore, Br substitution can significantly reduce the N traps of the films to inhibit nonradiative recombination, thereby improving the overall performance.…”

Structural, Electronic, and Optical Properties of Cs2SnX4 (X = Cl, Br, and I) Multilayers: A Density Functional Theory Study

“…At the same time, Cs atoms have little influence on E g , and the probability of electron transition generated by optical excitation is very small. For many compounds ABX (B ¼ Pb, Sn; X ¼ Cl, Br, and I), monovalent cation A contributes less to the Fermi level, such as inorganic Cs [39][40][41] and organic MA, [32] PDA, [42] etc. However, the sand p-states of Cs atoms in the high energy level of the CB have hybridization contributions.…”