Reduced Thermal Conductivity and Improved Stability by B-Site Doping in Tin Halide Perovskites

Area of Science:

• Materials Science
• Solid-State Physics
• Inorganic Chemistry

Background:

• Halide perovskites are emerging as thermoelectric materials due to their favorable thermal and electrical properties.
• Tin halide perovskites exhibit high thermoelectric performance (zT) and lower toxicity compared to lead-based counterparts.
• Improving the stability of tin halide perovskites is crucial for practical applications.

Purpose of the Study:

• To investigate the effect of germanium (Ge) substitution on the stability and thermoelectric properties of tin (Sn) halide perovskites.
• To understand the mechanisms behind enhanced stability and reduced thermal conductivity in Ge-doped CsSnI3.
• To explore the potential of mixed metal CsSn1-xGexI3 perovskite thin films for thermoelectric devices.

Main Methods:

• Synthesis of mixed metal CsSn1-xGexI3 perovskite thin films.
• Characterization of structural stability under ambient air exposure.
• Measurement of lattice thermal conductivity.
• Density functional theory (DFT) simulations to analyze phonon behavior.

Main Results:

• CsSn1-xGexI3 thin films demonstrated significantly improved stability, retaining the desired black orthorhombic phase after prolonged air exposure.
• Germanium substitution preferentially oxidized at the surface, protecting the bulk tin from oxidation.
• Lattice thermal conductivity was dramatically reduced to 0.26 ± 0.01 Wm^-1K^-1 for CsSn0.9Ge0.1I3 at 353 K.
• DFT simulations revealed that Ge doping introduces more low-frequency phonon modes, enhancing phonon scattering and reducing phonon group velocity and lifetime.

Conclusions:

• Partial substitution of Sn(II) with Ge(II) in CsSnI3 perovskites leads to enhanced ambient air stability.
• Ge doping is an effective strategy to significantly reduce lattice thermal conductivity in tin halide perovskites.
• The findings provide insights into the origin of reduced thermal conductivity and improved stability in B-site doped perovskites, paving the way for advanced thermoelectric materials.