SKM 2023 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 5: Materials in Energy Conversion: Mechanical Properties and Solid State Batteries

MM 5.6: Vortrag

Montag, 27. März 2023, 11:45–12:00, SCH A 215

Influence of interstitial Li on the electronic properties of Li_xCsPbI₃ for photovoltaic and battery applications — •Wei Wei^1,2, Julian Gebhardt^1,2, Daniel Urban^2,3, and Christian Elsässer^1,2,3 — ¹Cluster of Excellence livMatS, University of Freiburg, Germany — ²Fraunhofer Institute for Mechanics of Materials IWM, Freiburg, Germany — ³Freiburg Materials Research Center (FMF), University of Freiburg, Germany

The stability of crystalline CsPbI₃ with interstitial Li ions is investigated together with the effect that Li has on the electronic structure of the resulting compound Li_xCsPbI₃. We analyze this by two structural models for CsPbI₃ at room temperature, the cubic α phase and a distorted structure analogous to the γ phase (γ’ structure). The hypothetical α phase does thermodynamically not allow Li uptake and is likely to be structurally unstable for x>1/4, while adding Li up to x=1 in the γ’ structure is possible. In all cases, Li promotes structural distortions, namely tilting of bond angles Δ _Pb-I-Pb and Cs off-center displacements Δ r_Cs, which are increasing with the Li concentration.

Interstitial Li has the following effects on the electronic structure of CsPbI₃: i) the induced structural distortion leads to a significant increase of the band gap; ii) the screening of additional electrons in the conduction band leads to a small increase of the band gap; iii) the effect of Li 2s states on the band edges and band gap is negligible. Altogether, the change of the band gap is dominated by the tilting of Δ _Pb-I-Pb angles: stronger distortion caused by increasing Li content is accompanied by an increased band gap.