Thickness-Dependent Seebeck Coefficient in Hybrid 2-Dimensional layers

Abstract

The Seebeck coefficient in a single molecule is determined by the slope of the transport probability of the charge carrier at the Fermi level, which can result in high Seebeck coefficients. However, since single molecules can only generate a limited amount of power for thermoelectric applications. Hence, larger scale systems must be developed to provide enough power for real applications. In this work, we examine the effect of the dimensionality on the Seebeck coefficient of molecule/Au nanoparticle 2D arrays with a massive number of molecular junctions within the network system. This approach increases the complexity and interactions between the components as the system size scales. In this work, we observed that the multilayer structure of 2D hybrid arrays provides higher Seebeck coefficients than monolayer structures with same molecular linkers. In particular, Oleylamine (OAM) and thiolated anthraquinone derivatives (5AQ5) are used as molecular interlinkers between gold nanoparticles in the structure. Experimental results illustrate that a four-layer structure of OAM/Au 2D array yields a ~11x improvement in the Seebeck coefficient $(\mathrm{S}=38.21\quad \mu \mathrm{V}/\mathrm{K})$ over the single-layer structure $(\mathrm{S}=3.36\ \mu \mathrm{V}/\mathrm{K})$, which, along with an improvement in the conductivity yields a power factor improvement of 635 times. The other set of results illustrate that a three-layer structure of anthraquinone-based norbornylogous bridge (5AQ5)/Au 2D array yields a ~26x improvement in the Seebeck coefficient $(\mathrm{S}=-3254\ \mu \mathrm{V}/\mathrm{K})$ over the single-layer structure $(\mathrm{S}=-127\ \mu \mathrm{V}/\mathrm{K})$, and a power factor improvement of 177 times. These findings demonstrate that it is possible to improve the thermoelectric performance of engineered nanostructures by controlling the number of layers.