QM/MM investigation of the degradation mechanism of the electron-transporting layer

Abstract

The mechanism of charge transfer among tris(8-hydroxyquinolinate)aluminum (Alq3) molecules in the electron-transporting layer (ETL) under amorphous conditions was theoretically investigated using both quantum mechanical/molecular mechanical (QM/MM) calculations and molecular dynamics (MD) simulations. The rate constant of the electron transfer was estimated for the equilibrated structure taken from the QM/MM MD simulations, based on the hopping model and Marcus theory. It was found that the coordination of a (LiF)4 cluster in ETL drastically lowers the energy of the lowest unoccupied molecular orbital in the Alq3 molecule. The small rate constant, namely the slow charge mobility, in ETL is believed to be causally related to the low-lying delocalized unoccupied molecular orbital of Alq3 coordinated by the (LiF)4 cluster. The results suggest that their interaction has a considerable influence on efficiency and is attributed in part to ETL degradation in organic light-emitting diodes.