Fused arene-functionalized polyhedral oligomeric silsesquioxanes as thermoelectric materials

Abstract

Two derivatives of fused-arene functionalized polyhedral oligomeric silsesquioxanes (POSS-ANT and POSS-PDI-POSS) were synthesized by the reaction of aminopropylisobutyl POSS with either 9-anthracenecarboxylic acid or perylene-3,4,9,10-tetracarboxylic dianhydride. Proton NMR and FT-IR spectroscopies confirmed their purity and structures. The UV-visible and emission spectra of POSS-ANT and POSS-PDI-POSS in solution follow similar spectral patterns as their building blocks. These spectral signatures suggest that there is no interruption on the optical properties from POSS cages. Electrical characterization conducted by casting thin films either by spin coating or drop casting on glass substrates showed subohmic semiconductor behavior with electrical conductivity of 110.5 × 10⁻³ S cm⁻¹ for POSS-ANT and 11.76 × 10⁻³ S cm⁻¹ for POSS-PDI-POSS at room temperature. The temperature dependence IV curves obtained for the test devices prepared from drop casting of PDI-POSS-PDI exhibit a noticeable improvement in electrical conductivity with the highest conductivity of 115.3 × 10⁻³ S cm⁻¹ where as POSS-ANT shows no improvement in conductivity above the room temperature. From the temperature dependent surface morphology analysis and DSC traces, it is revealed that the microstructural morphology of the thin films determines almost all the electrical properties of both compounds. Thermoelectric measurement of POSS-ANT showed a maximum power factor of 2.8 μW K⁻² m⁻¹ and Seebeck coefficient of 160.85 μV K⁻¹ at room temperature where as POSS-PDI-POSS showed an improved thermoelectric performance above room temperature with a Seebeck coefficient of 140.30 μV K⁻¹ and a power factor of 1.7 μW K⁻² m⁻¹.