The effective thermal conductivity of a screen-printed thermoelectric film of Bi₂Te₃ and CsSnI₃

In recent years, printed thermoelectric thin films have attracted attention due to their advantages in enabling large-area and flexible designs. We developed printable thermoelectric composites of bismuth telluride and halide perovskite, which were expected to exhibit superior thermoelectric properties compared to other printable materials, such as conductive organic materials. The measured dimensionless figure of merit was about 0.1 at room temperature due to its low thermal conductivity. We assessed the interfacial thermal resistance between bismuth telluride and halide perovskite using multilayered films to understand the measured low thermal conductivity. The calculated thermal conductivity using the measured interfacial thermal resistance was fairly consistent with the effective thermal conductivity observed. We also discussed the interfacial thermal resistance using a phonon transport model based on ab-initio calculations to confirm the validity of our measurements. Additionally, we found that the high interfacial thermal resistance was achieved due to the low group velocities of both materials in the composites. This mechanism can be applied not only to improve thermoelectric materials but also to address thermal issues in composites.