Polymer and Hybrid Materials for Flexible Thermal Energy Harvesting

Polymer-based thermal energy harvesting technologies offer promising routes to convert low-grade heat into electricity using flexible platforms. Organic thermoelectric (TE) generators, quasi-solid-state thermogalvanic cells, and ionic TE devices are particularly attractive because polymeric materials combine low thermal conductivity with mechanical softness and solution processability. However, their output performance remains insufficient for practical power generation, necessitating advances in molecular design, charge/ion transport, interfacial reaction kinetics, and device-level integration. This presentation focuses on our recent progress in polymer and hybrid materials for flexible thermal energy harvesting. The first part centers on organic TE materials based on molecularly doped conjugated polymers. We introduce dopant design based on Lewis acid–base chemistry, in which Lewis acids coordinate with cyano-functionalized molecules to form highly electron-withdrawing Lewis-paired dopants for efficient and stable p-doping. The roles of dopant structure, solvent polarity, polymer–dopant interactions, and latent doping chemistry are examined in relation to charge transfer, electrical conductivity, and TE performance. A vacuum-filtration strategy using doped polymer suspensions is also described as a rapid and scalable route to thick, uniformly doped TE legs and compact organic TE generators. The second part covers quasi-solid-state thermogalvanic cells based on redox-active gel electrolytes and flexible hybrid electrodes. Metallized textile electrodes and engineered gel electrolytes are combined to enhance redox kinetics, ion diffusion, and power density. Finally, novel ionic TE systems are introduced, highlighting how polymer–ion interactions and soft ion-conducting networks can be engineered to generate large thermovoltages from small temperature gradients.