Investigating thermoelectric properties in conjugated polymer polyl thin films to achieve higher levels of performance

Organic thermoelectrics offer the potential to deliver flexible, low-cost devices that can directly convert heat to electricity. Huang et al. investigate the thermoelectric properties in conjugated polymer polyl, or PBTTT, films, which demonstrate high conductivity and a high thermoelectric power factor.

The researchers present a systematic study of what thermoelectric performance is achievable in this polymer system when inducing the alignment of the polymer chains in the direction of the current flow to boost electrical conductivities. They treat the film with a recently developed, more controlled and stable doping method based on exchanging the molecular dopant with a stable, nonreactive ion.

“It was very gratifying to see that such high levels of electrical conductivity could be achieved through a systematic optimization of the polymer alignment in this well-controlled polymer system,” said author Henning Sirringhaus.

“The system exhibited a very well-defined microstructure even when doped to high levels, and the process of alignment did not reduce the thermoelectric voltage, which is what often happens when attempting to enhance electrical conductivities,” said author Yuxuan Huang.

Since there are so many processing parameters that impact molecular structure in thin films, the researchers opted for statistical, design of experiment methods to enable a systematic exploration of the process optimization space while restricting the experiments to a feasible number.

“We hope that through the better understanding of the underpinning physics and through exploring the vast molecular design freedom that is available through organic synthesis within this class of materials, we will discover new materials with higher and higher levels of performance,” said Sirringhaus.

Source: “Design of experiment optimization of aligned polymer thermoelectrics doped by ion-exchange,” by Yuxuan Huang, Dionisius Hardjo Lukito Tjhe, Ian Jacobs, Xuechen Jiao, He Qiao, Martin Statz, Xinglong Ren, Xinyi Huang, Iain McCulloch, Martin Heeney, Christopher Robert McNeill, and Henning Sirringhaus, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0055886 .