Organic π-type thermoelectric module supported by photolithographic mold: a working hypothesis of sticky thermoelectric materials

Abstract

To examine the potential of organic thermoelectrics (TEs) for energy harvesting, we fabricated an organic TE module to achieve 250 mV in the open-circuit voltage which is sufficient to drive a commercially available booster circuit designed for energy harvesting usage. We chose the π-type module structure to maintain the temperature differences in organic TE legs, and then optimized the p- and n-type TE materials’ properties. After injecting the p- and n-type TE materials into photolithographic mold, we eventually achieved 250 mV in the open-circuit voltage by a method to form the upper electrodes. However, we faced a difficulty to reduce the contact resistance in this material system. We conclude that TE materials must be inversely designed from the viewpoints of the expected module structures and mass-production processes, especially for the purpose of energy harvesting.

Thermoelectric materials and applications for energy harvesting power generation

“…In view of possible compatibility with general semiconductor fabrication methods, a photolithography method was used to fabricate a π-type flexible organic module [99]. PEDOT:PSS and TTF-TCNQ were used as the p-and n-type materials, respectively.…”

“…An output voltage of 250 mV, sufficient to drive electrical devices with a booster circuit, was realized at 80 K temperature difference. However, the high contact resistance was a problem, and it was proposed to design thermoelectric materials from the standpoints of expected module structures and mass-production processes rather than optimize ZT of the material first [99].…”

A review on conductive polymers and their hybrids for flexible and wearable thermoelectric applications

“…Furthermore, photolithography has been used to manufacture flexible organic TEGs [223]. Satoh et al used PEDOT:PSS and TTF-TCNQ as p-type and n-type materials to manufacture thermoelectric legs for a π-type module structure.…”

“…An output voltage of 250 mV was obtained at ΔT = 80 K, which was enough to power selected devices, even if the addition of a booster circuit was required. However, high contact resistances, detrimental to the overall efficiency, were observed, and the authors underlined the needs to design materials from the viewpoints of device architecture and large-scale manufacturing rather than only focusing on the optimization of the materials for higher figures of merit (ZT) [223].…”

Improvement to the thermoelectric properties of PEDOT:PSS

“…The p-type material has holes as the majority charge carrier meanwhile electrons are the majority charge carriers within n-type materials. 27,32,33 As expressed in Figure 1.1.1, the holes and electrons will travel along the same direction away from the heat source towards the cold junction. As the carriers move along this path an electric field is generated whereby the current will flow.…”