posted on 2022-01-12, 06:13authored byMarco Carlotti, Saurabh Soni, Andrii Kovalchuk, Sumit Kumar, Stephan Hofmann, Ryan C. Chiechi
This paper describes
a simple model for comparing the degree of
electronic coupling between molecules and electrodes across different
large-area molecular junctions. The resulting coupling parameter can
be obtained directly from current–voltage data or extracted
from published data without fitting. We demonstrate the generalizability
of this model by comparing over 40 different junctions comprising
different molecules and measured by different laboratories. The results
agree with existing models, reflect differences in mechanisms of charge
transport and rectification, and are predictive in cases where experimental
limitations preclude more sophisticated modeling. We also synthesized
a series of conjugated molecular wires, in which embedded dipoles
are varied systematically and at both molecule–electrode interfaces.
The resulting current–voltage characteristics vary in nonintuitive
ways that are not captured by existing models, but which produce trends
using our simple model, providing insights that are otherwise difficult
or impossible to explain. The utility of our model is its demonstrative
generalizability, which is why simple observables like tunneling decay
coefficients remain so widely used in molecular electronics despite
the existence of much more sophisticated models. Our model is complementary,
giving insights into molecule–electrode coupling across series
of molecules that can guide synthetic chemists in the design of new
molecular motifs, particularly in the context of devices comprising
large-area molecular junctions.