High-performance organic thermoelectric materials based on n-type conjugated polymers via chemical isomerization-induced charge transport modulation

High-performance n-type conjugated polymer-based thermoelectric (TE) materials remain scarce, despite their critical necessity in realizing wearable TE generators. Here, we sought to optimize TE charge transport in the n-type conjugated polymer poly(benzodifurandione) (PBFDO) via the incorporation of the isomeric monomer, benzodipyrandione (BPDO). BFDO segments in the PBFDO chain were systematically converted to BPDO segments via chemical isomerization driven by hydrothermal treatment. Hydrothermal treatment decreased the carrier density, whereas the conversion of BFDO to BPDO improved the chain planarity and crystalline structure, featuring favorable electrical conduction. Moreover, the presence of BPDO segments transformed the transport mode of low-energy charge carriers from fluctuation-induced tunneling (FIT) to nuclear tunneling (NT). This energy-filtering effect significantly enhanced the Seebeck coefficient to 48 μV K^-1, yielding an n-type conjugated polymer with both a high power of 142 μW m^-1 K^-2 and a high electrical conductivity of 640 S cm^-1.