Three-dimensional kinetic Monte Carlo modeling of disordered organic semiconductor devices with molecular doping

Abstract

Molecular doping plays a pivotal role in enhancing the performance of organic light-emitting diodes, particularly by facilitating charge injection across large energy barriers at the electrode/organic interfaces. Recently, it has been shown that the Schottky-contact formation between metal electrodes and molecularly doped disordered organic semiconductors leads to modified charge-carrier mobilities compared to undoped bulk materials, smaller depletion widths than inorganic semiconductors, as well as ultraslow charge-carrier dynamics [Yu et al., Phys. Rev. Appl. 19, 024041 (2023)]. These results bring up the question whether conventional one-dimensional drift–diffusion approach can accurately model devices with doped injection layers. In this work, to gain a comprehensive understanding of the microscopic mechanisms involved, we systematically investigate disordered organic semiconductor devices with molecular doping using three-dimensional kinetic Monte Carlo simulations and compare with a one-dimensional drift–diffusion model. We find that for full-device simulations, (a) one-dimensional drift–diffusion approach overestimates current density (without special treatment of mobility in the doped layer); (b) one-dimensional drift–diffusion approach overestimates the depletion layer width; and (c) although the dynamics of carrier profiles could be slow (∼10−5 s), the device current density can reach a steady state much faster (∼10−6 s). The three-dimensional kinetic Monte Carlo simulations are employed to study both single doped layers and bipolar doped layers (P–N junctions) and are shown to well reproduce experimental current density–voltage characteristics.