Connectivity-driven bi-thermoelectricity in heteroatom-substituted molecular junctions

Area of Science:

• Molecular electronics
• Thermoelectric materials
• Quantum interference phenomena

Background:

• Improving the thermoelectric performance of molecular junctions is crucial for energy harvesting applications.
• Polyaromatic hydrocarbons (PAHs) are promising core structures, but their thermoelectric properties, particularly the Seebeck coefficient, need enhancement.
• Existing strategies often struggle to achieve significant and tunable Seebeck coefficients in molecular systems.

Purpose of the Study:

• To develop a new strategy for enhancing the Seebeck coefficient in polyaromatic hydrocarbon (PAH)-based molecular junctions.
• To explore the combined effects of destructive quantum interference and heteroatom substitution on thermoelectric properties.
• To demonstrate and utilize the novel 'bi-thermoelectric' property for advanced device design.

Main Methods:

• Utilized molecular engineering by combining specific connectivities that induce destructive quantum interference.
• Introduced heteroatom substitution into parent PAH molecules to modify electronic structure.
• Investigated the resulting changes in the mid-gap Seebeck coefficient through theoretical analysis and/or experimental measurements.

Main Results:

• Achieved a non-zero mid-gap Seebeck coefficient in daughter molecules derived from parent PAHs with vanishing Seebeck coefficients.
• Demonstrated a 'bi-thermoelectric' property where the sign of the Seebeck coefficient is connectivity-dependent.
• Developed simple, parameter-free rules for predicting the Seebeck coefficient, facilitating molecular design.

Conclusions:

• The combined strategy of destructive quantum interference and heteroatom substitution effectively enhances thermoelectric performance in molecular junctions.
• The discovered 'bi-thermoelectric' property is key for designing efficient tandem thermoelectric devices requiring both positive and negative Seebeck coefficients.
• The predictive rules offer a powerful and accessible tool for the rational design of next-generation molecular thermoelectric materials and devices.