Temperature dependence of charge transport in molecular ensemble junctions†

Abstract

Understanding charge transport across molecule–electrode interfaces is essential for advancing organic electronic devices, yet its underlying mechanisms remain incompletely understood. Here, we investigate the temperature dependence of conductivity in molecular junctions under various biasing regimes. By examining devices with both low and high current rectification, we identify the conditions leading to temperature-activated transport and the less common phenomenon where conductance decreases with increasing temperature. The current increase with temperature is consistent with previous findings in similar systems and is attributed to thermally assisted tunneling and incoherent tunneling processes. Notably, the discovery of the regime with a negative temperature coefficient for conductance provides the first experimental validation of theoretical frameworks that unify Landauer formalism with Marcus theory, which we attribute to entropic effects influencing the molecular conformation. These measurements have also captured the emergence of new electronic states arising from the co-assembly of molecules containing electron donor and acceptor moieties. Our results decipher key aspects related to charge transport in molecular junctions and leveraging these insights holds significant promise for accelerating the development of more complex devices that exploit electrode–molecule interfaces for tunable functionality.