Tailoring the framework of organic small molecule semiconductors towards high-performance thermoelectric composites via conglutinated carbon nanotube webs

Abstract

Recently, the thermoelectric (TE) properties of single-walled carbon nanotubes (SWCNTs)/polymer semiconductor composites have been dramatically improved; however, there are no examples of SWCNTs/organic small molecule semiconductor (OSMS) composites as TE materials, although OSMSs are more attractive due to their exact structure, easy structure optimization, high purity for performance optimization, etc. In this work, four p-type OSMSs are designed and synthesized as p-type binders for application in SWCNT-doped composite films. The relationship between TE properties and the structure including the conjugated-backbone and peripheral substituents is investigated. Photophysical spectroscopic and scanning electron microscopic studies indicate that the variation of molecular geometries and hybrid ratios results in obvious changes in the morphologies, interfacial contacts and grain boundaries of the composite films, subsequently affecting the TE properties of the samples. Notably, the SWCNT/TCzPy (1 : 1)-based hybrid film exhibits the best performance with an average power factor of 108.4 ± 4.8 μW m⁻¹ K⁻², which is three times higher than that of SWCNT/TDOPAPy. The results demonstrate that fine tuning the π-extensions of the central core or peripheral substituents of organic semiconductors is a good strategy for designing high-performance p-type organic small molecule TE materials.