Features of gate-tunable and photon-field-controlled optoelectronic processes in a molecular junction: Application to a ZnPc-based transistor

Abstract

Taking into account the fact that the transitions between the states of a molecular junction are carried out against the background of much faster relaxation processes in molecular terms and the conduction bands of electrodes, kinetic equations for integral occupancies of the molecular terms, as well as expressions for the time-dependent electronic current and radiation power of the fluorophore molecule, are obtained. Using the example of a molecular junction based on a ZnPc fluorophore, the transformation of a transient optoelectronic process into a stationary one is demonstrated. Corresponding analytical expressions are derived, including overall rates, which determine the characteristic times of establishing equilibrium current and light emission. The temporary process of the reorganization of the transmission channels dependently on the magnitude and polarity of the gate voltage as well as an external optical field is also demonstrated. The dependence of the overall rates on the elementary rates characterizing the recharge of the molecule, as well as radiation and nonradiative transitions in the molecule, is obtained. Estimates show that in a ZnPc-based transistor, the characteristic transition time is 10–100 ps if the current is in the range of 0.1–10 nA.