Roles of Polyethylenimine Ethoxylated in Efficiently Tuning Thermoelectric Performance of Poly(3,4-ethylenedioxythiophene)-rich Nanocrystal Film.

The regulation of oxidation level is of great importance as an efficient way to optimize the thermoelectric (TE) performance of conducting polymers. Many efforts have been devoted into the acquisition of high TE performance for PEDOT:PSS by oxidation/reduction post-treatment to achieve an effective compromise. However, a strong oxidant/reductant is usually employed to tune TE performance of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with high electrical conductivity ( σ) and Seebeck coefficient ( S), and also presents a number of operational challenges depending on fast reaction rate. Herein, a nontoxic polyethylenimine ethoxylated (PEIE) served as a reductant to successfully realize an enhanced S for PEDOT:PSS, followed as another significant anion-blocking role in enabling efficient modulation of oxidation level by sulfuric acid (H2 SO4 ) with a longer operating time. Eventually, a good PEDOT-rich nanocrystal is achieved by sequential dipping process in PEIE/ethylene glycol (PEIE/EG) and H2 SO4 solutions. A large TE power factor of 133 μW m-1 K-2 can be ascribed to the good formation of PEDOT-rich nanocrystal and an effective compromise between σ and S of PEDOT:PSS films. The mechanism was elucidated for efficient regulation of σ and S enabling high performance of organic TE materials.