Unified Mobility Model for Diffusion-Limited Current in Organic Diodes Based on Fermi-Dirac Statistics

The Fermi-Dirac statistics is adopted to consider degenerate effects in organic diodes. The degenerate drift-diffusion equation is analytically solved under the uniform-electrical-field approximation. The analytical expressions for the current-voltage relationship and carrier density are derived. The mobility model of Pasveer [Pasveer et al., Phys. Rev. Lett. 94, 206601 (2005)] is improved to consider correct characteristic length scales and combined with the analytical solution to analyze the properties of six organic diodes. The theoretical results are in good agreement with experimental data. Six model parameters are extracted for six devices, namely, the parameters N-0 and sigma for the density of states; the parameters mu(0) and a for the mobility model; and the potential barriers W-an and W-cat at the anode and cathode, respectively. The degenerate parameter (eta) over bar at 300 K is deduced. It is shown that two materials, MEH-PPV and F8BT, are degenerate. Although four other materials can be treated as nondegenerate, the degenerate effects are not negligible near the anode region.

Automated summary

The Fermi-Dirac statistics is used to consider degenerate effects in organic diodes, with analytical solutions obtained for the current-voltage relationship and carrier density. The mobility model is improved and applied to analyze six organic diodes, showing good agreement between theoretical results and experimental data. Two materials are found to be degenerate while degenerate effects near the anode region cannot be neglected for four other materials.