Achieving Boosted Thermoelectric Power Factor of MoS₂ Through Selective Charged-Impurity Free Doping

Ultrathin two-dimensional (2D) transition metal dichalcogenides (TMDs) exhibit unique band structures, characterized by a sharp density of states, large effective mass, and high valley degeneracy, making them ideal candidates for thermoelectric materials. To maximize the power factor (PF), surface charge-transfer doping (SCTD) has been widely applied to 2D TMDs, leveraging their ultrathin nature and surface sensitivity to enhance electrical conductivity. However, organic dopants introduced during the SCTD process often act as charged impurities, intensifying the trade-off between carrier concentration and the Seebeck coefficient, which degrades charge transport and lowers the thermoelectric PF.
In this presentation, we propose a charged-impurity free diffusion doping method for large-area 2D molybdenum disulfide (MoS₂) to surpass the conventional trade-off between carrier concentration and the Seebeck coefficient. In this method, organic dopants are selectively deposited onto the contact region of MoS₂ films using inkjet printing. Excess electrons diffuse from the contact region into the thermoelectric (TE) leg, driven by the difference in carrier concentration, increasing electrical conductivity without leaving undesirable charged impurities on the MoS₂ surface, thereby maximizing the PF. Our results show that this diffusion doping method minimizes charged impurity scattering, as confirmed by temperature-dependent electrical property measurements. Notably, the sharp decline in the Seebeck coefficient typically observed with conventional SCTD was suppressed, while electrical conductivity in large-area MoS₂ TE legs increased. We analyzed both electrical conductivity and the Seebeck coefficient by tailoring the concentration of organic dopants supported with theoretical calculations. By systematically optimizing doping conditions and device configurations, we achieved a record-high PF of 1698 µW/mK² in large-area MoS₂ thermoelectric generators (TEGs).