Heteroatom engineering enhancing thermoelectric power factor of molecular junctions

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 (C _n -SH, n = 5, 8, 11, 14) through heteroatom substitutions, including the terminal iodine (I) atom substitution and replacing backbone methylene units (-CH ₂ -) with oxygen (O) atoms, to obtain iodo-substituted oligo(ethylene glycol) thiolates (I-(C ₂ O) _m -C ₂ -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-(C ₂ O) _m -C ₂ -SH can be enhanced simultaneously compared to the length-matched SAMs of C _n -SH (n = 3m + 2), resulting in the PF of I-(C ₂ O) ₄ -C ₂ -SH being over 5 orders of magnitude higher than that of C ₁₄ -SH, which was attributed to the resonant states contributed from the substituted I-(C ₂ O) _m -C ₂ -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.