Space charge limited current in organic materials with free and trapped charges

The space charge limited current of amorphous organic semiconductors with an exponential density of states (EDOS-SCLC model) resembles the same dependence of bias with the trap limited current (TLC model) case. The similarity of these two current density formulas may course an overestimation of the influence of the free and trapped charges on current density when interpreting experimental data. We promote a transparent model incorporating both the influences of the free and the trapped charges on the current density. The model can be simplified into the EDOS-SCLC model and the TLC model in limiting conditions. When the influences of the free and the trapped charges are comparable, a transition of the slope of the current-voltage curve appears. When compared with experimental results, satisfactory agreement is obtained. What's more, the influence of dilution of narrow band materials into wide band matrix on the current density is discussed.