Seebeck Effect in Molecular Wires Facilitating Long-Range Transport

Area of Science:

• Molecular electronics
• Organic electronics
• Materials science

Background:

• Long-range charge transport in molecular wires is crucial for molecular electronics.
• Distinguishing charge transport mechanisms like tunneling and hopping is challenging with electrical characterization alone.

Purpose of the Study:

• To investigate the Seebeck effect in molecular wires to understand charge transport mechanisms.
• To examine the length dependence of the Seebeck coefficient in bis-terpyridine Ru(II) complex films.

Main Methods:

• Electrografting of bis-terpyridine Ru(II) complex films.
• Measurement of the Seebeck coefficient as a function of film thickness.
• Quantum-chemical calculations and Landauer-Büttiker probe simulations.

Main Results:

• The Seebeck coefficient increased with film thickness, reaching 1027 μV/K at 10 nm, with a rate of 95.7 μV/(K nm).
• Giant thermopower was attributed to the overlap of Ru complex molecular orbitals with the Fermi level.
• Length dependence indicated the Seebeck effect is dominated by coherent near-resonant tunneling.

Conclusions:

• The Seebeck effect is a powerful tool for elucidating charge transport mechanisms in molecular systems.
• Coherent tunneling, not thermal hopping, governs long-range charge transport in these Ru(II) complex films.
• This research contributes to the development of advanced molecular electronic and thermoelectric materials.