High-Energy Electron Beam-Induced Enhanced Thermoelectric Performance and Irradiation Resistance of PEDOT: PSS

Electron beam (EB) irradiation, a powerful method for electronic and molecular structure regulation of polymer materials, has been proven to be an effective strategy to boost the electrical conductivity (σ) of PEDOT: PSS. However, the irradiation damage from chain scission and cross-linking has an adverse effect on the mechanical and thermal performance. Herein, we propose a convenient approach to enhance irradiation resistance property by adding a chemical oxidant, ammonium persulfate (APS), into PEDOT: PSS, in which irradiation-induced fragmentations can be reaggregated via initiating free radical polymerization through APS. The PEDOT: PSS films doped with 5 wt % APS were exposed to 10 MeV EB irradiation at doses ranging from 2.5 to 20 kGy. The electrical conductivity of PEDOT: PSS-APS films reached 596 S cm^-1 at a dose of 2.5 kGy, 2 orders of magnitude higher than that of pure PEDOT: PSS films (4.94 S cm^-1), while the Seebeck coefficient remained nearly constant. An optimal thermoelectric power factor (PF) of 16.75 microW m^-1 K^-2 was achieved. The 1000-fold increase in carrier concentration (n) can elucidate the enhancement in the PF despite the deterioration of carrier mobility. During irradiation, more effective cross-linking occurred in PEDOT: PSS-APS films than in pure PEDOT: PSS. Structural characterization and DFT computational results implied that the imine or protonated amine brought by APS could not only improve the molecular structure but also narrow the band gap, which helped charge transport. The chain fragments caused by chain scission during irradiation could be polymerized via APS into new molecular chains, which influenced the transportation of charge carriers and resulted in enhanced thermal stability and mechanical properties of PEDOT: PSS-APS films. This work provides a simple and innovative treatment to improve both the thermoelectric property and the irradiation resistance of conducting polymers.