Defect Tolerance and Local Structural Response to 3d Transition-Metal Substitution in CsPbI3

Abstract

We present a systematic first-principles study of substitutional 3d transition-metal (TM) defects in CsPbI3 using the spin-polarized GGA+U framework. TM incorporation is generally energetically favorable and induces lattice distortions that are strongly localized around the defect site, preserving the overall structural integrity of the host. Analysis of defect formation energies and electronic structure shows that, with the exception of Sc and Ti, CsPbI3 exhibits a strong resistance to deep trap formation. Most TM substitutions instead introduce resonant states that hybridize with the band edges, consistent with the defect-tolerant nature of the material. While these states can modify the band gap, they do not generate isolated mid-gap traps. The observed distortions arise from strain-driven Van Vleck modes governed by ionic-radius mismatch, electronegativity differences, and TM-I orbital overlap, with amplitudes that decay rapidly away from the defect. Spin-polarized calculations reveal significant TM-induced spin polarization on the ligands and, in some cases, on neighboring Pb atoms, reflecting variations in covalency and hybridization across the 3d series. Together, these results establish a unified picture in which local structural response, electronic hybridization, and spin polarization jointly control the stability and electronic impact of TM defects in CsPbI3 , identifying dopants that are electronically benign or detrimental.

Figures (10)

• Figure 1: Stability polygon showing the stable region for CsPbI$_3$ enclosed by competing phases.
• Figure 2: Workflow demonstrates the methodology adapted for this study.
• Figure 3: (a): Defect formation energies in I-poor (left) and I-rich (right) shows Mn is the most stable defect with lowest formation energy. (b) Absolute difference of DFEs in I-rich and I-poor environment indicating dependence of defects on growth conditions.
• Figure 4: Strain driven dsitortions in local environment. (a) Left: Schematic showing the regular octahedrons in pristine CsPbI$_3$ Right: Shrinked TM octahedron and distorted PbI$_6$. (b) Distortion magnitude of the PbI$_6$ octahedron adjacent to TM octahedron. Markers x and + indicate +2 and +1 oxidation states, respectively.
• Figure 5: Trends and anomalies observed for defected perovskites. (a) TM-I bond length vs ionic radii showing a deviation from linear trend. (b) Bader charge analysis giving insights into bonding nature between TM and I. (d) Increase in magnetization with number of unpaired electrons with Cr as exception where colorbar $\Delta$ magnetization is the difference between total and absolute magnetizaiton. Markers x and + indicate +2 and +1 oxidation states, respectively.