Extrapolation method for reliable measurement of Seebeck coefficient of organic thin films

Measurement of the Seebeck coefficient of an organic thermoelectric (TE) thin film necessitates the accurate measurement of the temperature difference across the film. However, direct measurement of temperature difference is difficult for a small-gap organic TE device, which is favored for the high-resistance organic materials. Here, the effect of a nonlinear temperature distribution on the Seebeck coefficient measurement of organic TE films was systematically investigated to enable clear identification of the Seebeck coefficient for an organic TE film. The nonlinear temperature distribution across an organic TE device was analyzed by a finite-element analysis simulation and IR thermal imaging. The nonlinear temperature distribution resulted in a difference between the measured temperature difference and the actual temperature difference across the organic TE film. The conventional interpolation method significantly overestimated the Seebeck coefficient when the temperature distribution was nonlinear. To reduce the measurement error, the ideal Seebeck voltage was extrapolated from a series of Seebeck voltages measured at different position in the edge-contacted device configuration. The ideal Seebeck coefficients of various organic TE films with a wide range of electrical conductivities were determined successfully, and the Seebeck coefficient measured by extrapolation method was not affected by the geometry of the organic TE film.