Control of electroluminescence in a molecular photodiode by gate voltage

Abstract

The role of the gate voltage in the regulation of electroluminescence (EL) of a molecular photodiode with asymmetric localization of electron density on the frontier highest occupied and lowest unoccupied molecular orbitals of the photochromic molecule is considered. It is shown that the gate voltage can have a significant effect on the formation of EL in devices where one of the orbital energy levels are outside the gap between the biased Fermi levels of the electrodes. The role of the gate voltage consists in shifting the position of the orbital energy levels until both frontier levels fall into the gap and thereby provide a resonant mechanism for the formation of EL. This leads to the inclusion of EL at a lower bias voltage than that which includes EL at zero gate voltage. In addition, the shift in energy levels caused by the gate voltage explains the mechanism for controlling the kinetics of bipolarity formation. The effect is carried out by turning on and off the resonant hopping’s of the electron between the conducting states of the electrodes and molecular orbitals localized at different distances from the electrode surfaces.