Conductivity decay in freshly fabricated TFB films

Abstract

Understanding the hole transport layers is fundamental to improve the stability of quantum-dot light-emitting diodes. This study investigates the short-term conductivity decay of freshly fabricated poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl))diphenylamine) (TFB) films under applied voltage. In addition, the conductivity decay of freshly prepared TFB films can be partially recovered after short-term storage. The phenomenon is also observed in other hole transporting materials, such as PVK and PF8Cz. The decay dynamics can be described using the Kohlrausch–Williams–Watts stretched-exponential function. The temperature-dependent relaxation time extracted from the decay curves obeys an Arrhenius law, yielding an activation energy of 0.18 ± 0.03 eV. This value is in good agreement with the calculated reorganization energy associated with the hopping transport of charge carriers. Based on the results, conductivity decay of freshly fabricated TFB films during the initial short-term period can be explained by the coupling between electric field-induced polarization and carrier transport (denoted as polarization–conduction coupling).