Organometallic halides are great candidates for optoelectronics. As an important family of semiconductors, understanding their thermoelectric transport properties is also important. This has been a challenging task as many of such compounds are highly intrinsic. In this work, we synthesized two halides, CH3NH3PbI3 and (CH3NH3)3Bi2I9, using a solvent-free method. We found an extraordinarily high Seebeck coefficient of +2600 ± 200 μV/K in (CH3NH3)3Bi2I9. For CH3NH3PbI3, our synthesis method led to a negative Seebeck coefficient of −1350 ± 50 μV/K, in contrast to positive values observed in solvent synthesized samples. We also found the thermal conductivity of CH3NH3PbI3 to be 0.38 W/m K, largely independent of temperature from 300 K to 450 K, despite a tetragonal-to-cubic phase transition. (CH3NH3)3Bi2I9 has an even lower thermal conductivity of 0.21 W/m K (also temperature independent) which is due to its soft phonon dispersion and weak bonds.
Thermoelectric materials have been extensively studied for applications in solid-state power generation and cooling. Progress has been made over the past decade in multiple materials systems, hence, it becomes increasingly...
Seebeck coefficient is a widely studied semiconductor property. Conventional Seebeck coefficient measurements are based on DC voltage measurement. Normally this is performed on samples with moderate resistances (e.g., below a few MΩ level). Certain semiconductors are intrinsic and highly resistive. Many examples can be found in optical and photovoltaic materials. The hybrid halide perovskites that have gained extensive attention recently are a good example. Despite great attention from the materials and physics communities, few successful studies exist of the Seebeck coefficient of these compounds, for example CH3NH3PbI3. An AC‐technique‐based Seebeck coefficient measurement is reported, which makes high‐quality Seebeck voltage measurements on samples with resistances up to the 100 GΩ level. This is achieved through a specifically designed setup to enhance sample isolation and increase capacitive impedance. As a demonstration, Seebeck coefficient measurement of a CH3NH3PbI3 thin film is performed at dark, with sample resistance 150 GΩ, and found S = +550 µV K−1. The strategy reported could be applied to the studies of fundamental transport parameters of all intrinsic semiconductors that have not been feasible.
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