Conductivity Decay in Freshly Fabricated TFB Films

Understanding the hole transport layers is fundamental to improve the stability of quantum-dot light-emitting diodes (QLEDs). 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 phenomena is also observed in other hole-transporting materials, such as PVK and PF8Cz. The decay dynamics can be described using the Kohlrausch-Williams-Watts (KWW) stretched-exponential function. The temperature dependent relaxation time extracted from the decay curves obeys an Arrhenius law, yielding an activation energy of $0.18\pm0.03~ \mathrm{eV}$. 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 to the coupling between electric field-induced polarization and carrier transport (denoted as polarization-conduction coupling).