Thermodynamic Design Strategy for Ionic Thermoelectric Polymer Complexes with Giant Thermopower and Power Density

Ionic thermoelectric (TE) materials offer great promise for self‐powered wearable electronics due to their ability to convert low‐grade heat into electricity with ultrahigh thermovoltages. However, their performance remains limited by an incomplete understanding of the thermodynamic factors governing ionic TE efficiency. Here, a thermodynamically guided design strategy is reported for high‐performance p‐ and n‐type ionic TE polymer complexes. By tailoring the interplay between ions and polymer matrices through controlled synthetic approaches, record‐high ionic figures of merit ( ZT i ) of 49.5 and 32.2 are achieved, and outstanding normalized power densities of 46.7 and 79.0 mW·m −2 ·K −2 . A flexible p/n‐type ionic TE module delivers a remarkable voltage output of 1.03 V·K −1 and a normalized power density of 981 mW·m −2 ·K −2 . This module powers a commercial LED under a temperature gradient of just 1.5 K, without external amplification. These results offer a practical and scalable path toward wearable energy harvesting systems based on ionic TEs.