A new study has proposed a one-step "cleaving and doping" strategy that enhances both the thermoelectric (TE) performance and stability of open-shell conjugated polymers. The research demonstrates an approach to achieving highly ordered molecular packing and efficient doping without the need for additional dopants.

Led by researchers from the Shanghai Institute of Ceramics of the Chinese Academy of Sciences, in collaboration with other partners, the study was recently published in Angewandte Chemie International Edition.

Open-shell conjugated polymers are regarded as promising materials for TE applications due to their unique electronic structures. However, their practical application has been hindered by structural disorder and poor stability in air and at high temperatures.

To address these challenges, the researchers treated three benzo[1,2-c;4,5-c']bisthiazole (BBT)-based polymers with trifluoromethanesulfonic acid (TfOH). This acid simultaneously cleaves the silane side chains of the polymers and dopes their backbones in situ.

The synergy between enhanced carrier mobility and optimized carrier concentration has led to an improvement in thermoelectric performance compared with the corresponding alkyl polymer. Beyond performance gains, the side-chain-free films exhibit excellent stability in air and at elevated temperatures, retaining their power factor even after prolonged heating at 100°C for four hours.

Grazing incidence wide-angle X-ray scattering results indicate that the removal of side chains significantly reduces lamellar and π-π stacking distances, thereby facilitating efficient intra- and intermolecular charge transport.

Density functional theory calculations suggest that the trifluoromethanesulfonate (TfO-) anions are thermodynamically positioned near the positive potential of the thiophene units, effectively doping the polymer without disrupting its close chain packing. The dense and ordered molecular packing resulting from side-chain removal is identified as the key factor driving the enhanced TE performance and stability.

This study highlights that one-step side-chain cleavage and in situ doping provides a viable pathway to fabricate stable, high-mobility conjugated polymer films. Its potential applications extend beyond TEs to a wide range of organic electronic devices.