Tackling Challenges in Seebeck Coefficient Measurement of Ultra-High Resistance Samples with an AC Technique.

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 low resistances below a few Mohm level. Meanwhile, certain semiconductors are highly intrinsic and 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. Few credible studies exist on the Seebeck coefficient of, CH3NH3PbI3, for example. We report here an AC technique based Seebeck coefficient measurement, which makes high quality voltage measurement on samples with resistances up to 100Gohm. This is achieved through a specifically designed setup to enhance sample isolation and reduce meter loading. As a demonstration, we performed Seebeck coefficient measurement of a CH3NH3PbI3 thin film at dark and found S = +550 microV/K. Such property of this material has not been successfully studied before.