Noise and Thermodynamic Uncertainty Relation in "Underwater" Molecular Junctions

TL;DR

This paper investigates charge current noise and thermodynamic uncertainty relations in molecular junctions and photovoltaic cells, revealing classical-quantum analogies and bounds on efficiency in energy conversion processes.

Contribution

It introduces a classical master equation approach to analyze noise and TUR in molecular and photovoltaic systems, connecting classical and quantum descriptions and predicting efficiency limits.

Findings

Classical current noise mirrors quantum structure due to charge correlations.

Derived TUR bounds relate current, fluctuations, and entropy in electrochemical junctions.

Predicted upper efficiency bounds for photovoltaic energy conversion.

Abstract

We determine the zero-frequency charge current noise in a metal-molecule-metal junction embedded in a thermal environment, e.g., a solvent, dominated by sequential charge transmission described by a classical master equation, and study its dependence of specific model parameters, i.e., the environmental reorganization energy and relaxation behavior. Interestingly, the classical current noise term has the same structure as its quantum analog which reflects a charge correlation due to the bridging molecule. We further determine the thermodynamic uncertainty relation (TUR) which defines a bound on the relationship between the average charge current, its fluctuation and the entropy production in an electrochemical junction in the Marcus regime. In a second part, we use the same methodology to calculate the current noise and the TUR for a protoype photovoltaic cell in order to predict its upper bound for the efficiency of energy conversion into useful work.