Electron Transport in a Fluorine-Based Copolymer: Evidence for the Absence of Correlated Disorder

Abstract

Spatial correlation between two unordered transmission site energies of semiconducting polymers applied to organic electronic devices can impact the charge carrier mobility (CCM). It has been uncertain if this spatial correlation exists in relevant polymers. This study focuses on electronic transmission in a fluorene-based copolymer called poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)](F8BT) commonly applied to polymer light-emitting diodes (PLEDs). In terms of the F8BT-based electron-only device (EOD), the layer thickness dependence (Ltd.) of the current density is analyzed. Two models are adopted, with the intention of depicting the electronic transmission: the improved extended Gaussian disorder model(IEGDM) and extended correlated disorder model (ECDM). The IEGDM considers the dependence of the CCM upon electric field, temperature, and carrier density, incorporating the influences of Arrhenius and non-Arrhenius temperature dependence. In addition, the ECDM includes or excludes the spatial correlations between two site energies. Current-voltage J – V features are analyzed using IEGDM and ECDM. The two models provide eminent fits. A contrast between the parameters of the models reveals a more practical intersite distance by IEGDM (1.3 nm) than the value by ECDM (0.4 nm). This suggests that correlations between the site energies may not be significant or may be absent. Therefore, through the analysis, the evidence is provided for the absence of correlated disorders.