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

TL;DR

This study uses first-principles calculations to analyze how 3d transition-metal defects affect the structure and electronic properties of CsPbI3, revealing its defect tolerance and the effects of various dopants.

Contribution

It provides a comprehensive first-principles analysis of 3d transition-metal substitution effects in CsPbI3, highlighting defect tolerance mechanisms and electronic impacts.

Findings

Most TM substitutions do not create deep traps.

Defects induce localized lattice distortions that decay rapidly.

Certain dopants cause spin polarization and hybridization effects.

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.