Simultaneously enhancing the mechanical and thermoelectric properties of diketopyrrolopyrrole-thiophene based conjugated polymers through dynamic hydrogen-bonding

Abstract

Remarkable progress has been made in the development of thermoelectric materials based on diketonepyrrolopyrrole-thiophene (DPPT). However, achieving DPPT polymers with both high thermoelectric and mechanical properties remain a challenge. In this study, thymine groups, which are beneficial for the formation of intermolecular hydrogen bonds, were introduced into the side chains of DPPT, and a series of polymers (PDPPT-x) with different amount of thymine groups (x is the molar ratio of thymine side chains) were synthesized and characterized. The introducing thymine groups can regulate the self-assembly of conjugated polymers, effectively enhancing the crystallinity and molecular packing order, and thereby improve the charge carrier mobility. Additionally, the formed dynamic hydrogen-bonding networks by the thymine groups possess a moderate strength that can alleviate applied pressure and enhance the flexibility. Among these polymers, PDPPT-5 exhibited superior performance with excellent flexibility demonstrated by its elongation at break (up to 19.8 %), surpassing that of PDPPT-0 by a power factor of 2.2. In addition, the incorporation of 5 % amount of thymine groups can enhance the interchain interactions, thereby improving the crystallinity of the polymers and consequently enhancing the carrier mobility (4.26 × 10-3 cm2 V−1 s−1 for PDPPT-5 compared to 1.14 × 10-3 cm2 V−1 s−1 for PDPPT-0). Upon doping with FeCl3 at room temperature, the power factor of PDPPT-5 is about twice that of PDPPT-0. These results suggest that incorporating hydrogen bonding is a highly effective strategy for enhancing both the thermoelectric and mechanical properties of conjugated polymer-based thermoelectric materials.