Correcting for contact geometry in Seebeck coefficient measurements of thin film devices

Abstract

Driven by promising recent results, there has been a revived interest in the thermoelectric properties of organic (semi) conductors. Concomitantly, there is a need to probe the Seebeck coefficient S of modestly conducting materials in thin film geometry. Here we show that geometries that seem desirable from a signal-to-noise perspective may induce systematic errors in the measured value of S, S-m, by a factor 3 or more. The enhancement of S-m by the device geometry is related to competing conduction paths outside the region between the electrodes. We derive a universal scaling curve that allows correcting for this and show that structuring the semiconductor is not needed for the optimal electrode configuration, being a set of narrow, parallel strips.<p>Funding Agencies|Dutch program NanoNextNL</p

Accurate on-chip measurement of the Seebeck coefficient of high mobility small molecule organic semiconductors

“…This is to avoid contributions to the thermo-voltage from outside the active area, which can cause the Seebeck coefficient to be overestimated. 22 The crystalline domains are observed using Atomic Force Microscopy (AFM) to be up to 1 µm in diameter (Figure 1(b)). Top contacts are evaporated through a shadow mask (7 nm of MoO 3 and 25 nm of Au).…”

Explaining the effects of processing on the electrical properties of PEDOT:PSS

“…We believe that these relatively large values have, apart from lab-to-lab and batch-to-batch variations, to do with the used contact geometry as discussed in detail in Ref. [17]. …”

“…The device geometry used in our experiments is expected to give rise to an overestimation of S by a factor 1.3 according to Ref. [17]. The Seebeck coefficients reported here are corrected by this factor.…”

“…The Seebeck coefficient was also measured by the Keithley 2636a source measure unit [17]. A schematic of the experimental setup is shown in Fig.…”

Progress in Polymer Thermoelectrics

“…For instance, Seebeck coeicient can vary signiicantly, when electrodes with diferent geometries are used during the measurement. It was shown, that variation in electrode geometry can inluence Seebeck coeicient by a factor of 3 or more [74]. Regarding electrical conductivity, it is known that diferent methods, for example, van der Pauw or linear 4-point-probe, can result in diferent sheet resistances because of possible anisotropies in the samples.…”