Revealing the mechanism of carrier transport in host-guest systems of organic materials with a modified Poisson and drift-diffusion solver

A numerical solver based on two-dimensional Poisson and drift-diffusion equations with Gaussian-shaped density of states, the Poole-Frenkel field mobility model, and the Ising model are proposed to analyze carrier transport in the host-guest systems based on organic semiconductors. To investigate the performance of this solver, a series of the electron-only devices and hole-only devices are fabricated with different dopant concentrations. The space-charge-limited current model is applied to the simulation results to calculate the mobility. In addition, experimental results for different host-guest systems are compared to prove the accuracy of the solver. The solver is able to explain the physical mechanisms in different situations. At lower dopant concentrations, the guest states act as traps. Carriers are localized in these guest states, and the carrier mobility decreases dramatically. At the higher dopant concentrations, regions of guest material are able to connect with each other, and carriers have a probability to hop through the guest states. The mobility characteristics gradually approach those of the pure guest material.