Cotunneling assisted nonequilibrium thermodynamics of a photosynthetic junction

Abstract

We theoretically investigate a photosystem II-based reaction center modeled as a nonequilibrium quantum junction. We specifically focus on the electron–electron interactions that enable cotunneling events to be captured through quantum mechanical rates due to the inclusion of a negatively charged many-body state. Using a master equation framework with realistic spectral profiles, we analyze the cotunneling assisted current, power, and work. Amplification of the cotunneling assisted current and power occurs over a narrower bias range, reflecting a trade-off where a higher flux is compensated by a reduced work window. We further report that the cotunneling-enhanced thermodynamic variables, particularly within specific bias windows, depend on the interplay between cotunneling amplitudes, electron transition rates, and interaction energy. Both attractive and repulsive electronic interactions can enhance cotunneling, but this effect is sensitive to the energy balance between states and the tunneling strength asymmetries.