Effects of Post-treatment on the Transport Properties of Te/PEDOT:PSS and Ag₂Te/PEDOT:PSS Hybrid Thermoelectric Thin Films

Hybrid organic/inorganic materials composed of tellurium (Te) nanowires (NWs) embedded into poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) have been prominently studied after it was reported that their transport properties could be tuned by varying the length of the NWs and modulating the amount of PEDOT:PSS incorporated into the system.[1] Nevertheless, the influence of each constituent on the observed transport properties was not fully understood. Recently, based on molecular dynamics simulations and density functional theory calculations, it was proposed that the templating effect of PEDOT over the Te NWs surface is responsible for the enhanced transport properties of Te/PEDOT:PSS hybrids, and it was later experimentally demonstrated that the electronic transport occurs predominantly through the organic portion of the hybrid.[2,3] However, no direct experimental evidence of the existence of the templating effect was given.<br/><br/>It is well known that the electrical conductivity of conducting polymers (CPs) can be considerably enhanced when subjected to post-treatment processes, such as primary (i.e. charge transfer or acid-base processes) or secondary (morphological rearrangement that only impacts mobility and not oxidation level) doping. The transport properties strongly depend on the creation of polaron/bipolaron clusters dispersed through the polymer matrix, so their concentration and mobility are dependent on the oxidation level and the degree of crystalline domains.<br/><br/>In this work, we investigate the effects of tetrakis(dimethylamino)ethylene, sulfuric acid, and ethylene glycol post-treatments on the thermoelectric performance of p-type Te/PEDOT:PSS and n-type Ag₂Te/PEDOT:PSS hybrid materials. By analyzing the materials with X-ray diffraction, Raman spectroscopy, hard X-ray photoelectron spectroscopy, and Hall measurements, we find that variations of the thermoelectric performance are related to modifications in the morphological and chemical structure of PEDOT:PSS that is reflected in changes to the charge carrier density and mobility. Additionally, we present experimental evidence that strongly supports the templating effect causing the planar alignment of the first few layers of PEDOT over the NWs surface.<br/><br/>[1] Yee, S., <i>Phys. Chem. Chem. Phys.</i>, 2013, 15, 4024-4032.<br/>[2] Kumar, P., <i>Nat. Commun.</i>, 2018, 9, 5347.<br/>[3] Yang, L., <i>Sci. Adv.</i>, 2021, 7, eabe6000.