Ultra-high Seebeck coefficient and low thermal conductivity of a centimeter-sized perovskite single crystal acquired by a modified fast growth method

A centimeter-sized organic-inorganic hybrid lead-based perovskite CH₃NH₃PbI₃ (MAPbI₃) single crystal was obtained by using a modified fast and inverse-temperature growth method. The optical properties of this single crystal at room and low temperatures were studied in terms of optical absorption and photoluminescence measurements. The single crystal exhibited optical properties with a band-gap of 1.53 eV, which is comparable to a reported value. The temperature-dependent UV-vis spectra of this perovskite single crystal showed a unique structural phase transition as the temperatures varied. The thermoelectric properties of this MAPbI₃ single crystal were studied, showing that the Seebeck coefficient of 920 ± 91 μV K⁻¹ almost remained unchanged from room temperature to 330 K and it progressively increased with the increase in temperature and reached 1693 ± 146 μV K⁻¹ at 351 K. In contrast, there was no very clear trend for thermal conductivities with changes in temperature. The thermal conductivities were maintained between 0.30 and 0.42 W m K⁻¹ in the temperature range of 298-425 K. These thermoelectric characteristics would be useful for potential thermoelectric applications if the electrical conductivity of this crystal is improved by tuning its composition.