Investigating Thermoelectric Stability under Encapsulation Using PEI-Doped CNT Films as a Model System

Abstract

The stability of organic semiconductors is an important topic, which in the case of organic thermoelectrics (OTEs), has not yet got the attention it deserves. This work presents a simple method which allows to characterize the stability of OTEs, using patterned ITO substrates to electrically contact encapsulated samples. The method is applied to n-doped carbon nanotube films, a well-suited reference system due to their sensitivity to changes in doping level, and used to compare the effectiveness of different encapsulation methods. In the observed films, oxygen adsorption leads to a gradual p-doping. Among the investigated barrier materials, glass performs best. Flexible alternatives like transferred films of barrier polymers also show promise, while barrier films deposited by dropcast performed worse, likely due to their inhomogeneity. Finally, Raman imaging is shown to be a useful technique to investigate degradation in OTEs.