LAUSR

Thermoelectric (TE) materials are significant for sustainable development because they can be used to harvest waste heat into electricity. Organic TE materials have unique merits including high mechanical flexibility, low cost, and low intrinsic thermal conductivity. But their TE properties particularly the Seebeck coefficient are notably lower than the inorganic counterparts. Here, a poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) film is reported with a very high Seebeck coefficient and figure of merit (zT) at room temperature through secondary doping, dedoping engineering, and ionic energy filtering. The PEDOT:PSS films are successively treated with acid, base, and vitamin C that is a reductant, and then coated with 1‐ethyl‐3‐methylimidazolium dicyanamide (EMIM:DCA) that is an ionic liquid. This can exhibit a record‐high Seebeck coefficient and power factor of 111 µV K−1 and 1285 µW m−1 K−2, respectively, and the corresponding zT value is 1.05. This is the highest zT value for polymers and polymer composites, and it is comparable to that of the best inorganic TE materials.