An improved method for extraction of mobility from space charge limited current in organic semiconductor films

Estimation of mobility in thin film organic semiconductors from steady state current-voltage characteristics using Murgatroyd expression is attractive because of its simplicity but is accompanied by significant errors. These errors, resulting from neglecting diffusion current, are especially large at lower applied voltages, being more than 50% for voltages under 5 V. Using higher voltages to reduce errors is impractical in organic thin films not only due to possibility of degradation of the device but also due to distortion arising from parasitic series resistance caused by higher device currents. The present work describes an improved expression of space charge limited current for field dependent mobility that incorporates the effect of diffusion by modifying the quadratic dependence of J on voltage to J ∝ V ( V + V β ), where inclusion of voltage term V β compensates for neglecting diffusion current. Since the diffusion related voltage V β depends on small built-in voltage that may be present under expe...