Abstract
Engineering power factor (PF) of molecular junctions is one of the most attractive research in the field of thermoelectronics for the applications in thermal management and high-performance thermoelectric energy conversion at the nanoscale. Here, we modified the chemical structure of self-assembled monolayers (SAMs) formed by the widely investigated alkanethiolate (Cn-SH, n = 5, 8, 11, 14) through heteroatom substitutions, including the terminal iodine (I) atom substitution and replacing backbone methylene units (-CH2-) with oxygen (O) atoms, to obtain iodo-substituted oligo(ethylene glycol) thiolates (I-(C2O)m-C2-SH, m = 1, 2, 3, 4). We carried out the electrical tunneling and thermoelectric measurements based on the eutectic Ga-In technique (EGaIn) and found that the electrical conductance (G) and Seebeck coefficient (S) of the SAMs with I-(C2O)m-C2-SH can be enhanced simultaneously compared to the length-matched SAMs of Cn-SH (n = 3m + 2), resulting in the PF of I-(C2O)4-C2-SH being over 5 orders of magnitude higher than that of C14-SH, which was attributed to the resonant states contributed from the substituted I-(C2O)m-C2-SH near the Fermi energy. This study underscored the significance of chemically engineering the organic molecules to dramatically boost PF of molecular junctions for the further applications of high-efficient nanoscale thermoelectric devices.