Analysis of Hole Transport in Disordered Semiconducting Polymers: Uncorrelated Disorder Against Correlated Disorder

In this paper, the hole transport and spatial correlations between the transport site energies in conjugated polymer poly (2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene) (MDMO-PPV) are investigated. From an analysis of the layer thickness and temperature dependence of the current density-voltage (J-V) characteristics of MDMO-PPV hole-only devices, it is found that consistent descriptions with equal quality are obtained using both the improved extended Gaussian disorder model (IEGDM) and the extended correlated disorder model (ECDM), within which spatial correlations between the transport site energies are absent and are included, respectively. Based on a comparison of the model parameters from both models, we view the more realistic intersite distance obtained using the IEGDM (1.78 nm) compared to the value obtained using the ECDM (0.29 nm) as an indication that in MDMO-PPV correlations between the transport site energies are absent. Furthermore, we demonstrate that the mobility in organic semiconductors is carrier concentration dependent, and the effective mobility in a thin device is obviously higher than that in a thick device. Both the maximum of carrier concentration and the minimum of electric field appear near the interface of MDMO-PPV hole-only devices.