Unusually High Thermopower in Molecular Junctions from Molecularly Induced Quantized States in Their Semimetal Leads

The efficiency of a thermoelectric (TE) device depends on the extent to which its electron/hole transport symmetry at the Fermi level is broken. This requirement makes molecular junctions promising for TE applications as their transmission characteristics are highly nonlinear. Yet, in the absence of an efficient method to tune the position of the Fermi level within their transmission landscape, the typical Seebeck values of metal-molecules-metal junctions are |<i>S</i>| ≤ 100 μV/K, while considering their electrical and thermal conductance, it should be |<i>S</i>| ≥ 1 mV/K to be relevant for applications. Here, we report metal-molecules-semimetal junctions with |<i>S</i>| in the required mV/K range. This is achieved by molecularly induced quantized two-dimensional (2D) interfacial states within the semimetal that result in nonlinear features in their transmission properties. The importance of the presented approach goes beyond TE applications as it demonstrates a novel strategy to form and tune 2D interfacial layers within bulk materials by molecular monolayers.