Luminescence properties of poly(9,9-dioctylfluorene)/polyvinylcarbazole blends: Role of composition on the emission colour stability and electroluminescence efficiency

Abstract

Light-emitting diodes (LEDs), based on blue-emitting polyfluorenes are usually prone to the appearance of a contaminant green emission (centered around 520 nm), leading to an apparent whitish light emission. We find that, for LEDs based on poly(9,9-dioctylfluorene), PFO, the blending with the hole transporting polyvinylcarbazole, PVK, can suppress such green emission. LEDs based on a PFO/PVK blend with a 1:2 weight ratio and with aluminum cathodes show a quite stable blue emission. This result reveals the important role played by the interchain interactions on the observed contaminant green emission. In addition, we observe that in Al-based devices blending A c c e p t e d m a n u s c r i p t 2 causes a decrease in EL efficiency while in Mg-based devices we obtained higher efficiencies with the blend PFO:3PVK when comparing with neat PFO-based devices.

Insights on photophysical proprieties of DCM dye in PVK host matrix

“…Since the concentrations of DCM that we studied were much smaller with respect to PVK, the average distance between DCM and PVK molecules was not small enough (for the lowest concentrations) to produce a Dexter type energy transfer, which is the common mechanism for triplet energy transfer. Therefore, a Forster type energy transfer is the most probable in principle in this system with small concentration of dopants and it has been confirmed also from our time resolved measurements .…”

Enhancement of efficiency of multilayer polymer light-emitting diodes by inserting blocking layers

“…The lower energy transition of excimer emission becomes more significant when the emitter is prepared from a thin film to a multilayer EL device [27]. Further, the defect emission in the case of PFOs for longer wavelength emissions either originates from the chemical reaction between the PFO and diffused metal ions from the cathode [28][29][30] or is caused by keto defects generated by the oxidation of fluorene rings [31,32]. Fig.…”

Enhanced Optoelectronic Properties of PFO/Fluorol 7GA Hybrid Light Emitting Diodes via Additions of TiO2 Nanoparticles

“…Despite recent advancement, conjugated polymers, which are well known as active materials in various photovoltaic [ 1 , 2 ] and electroluminescence [ 3 , 4 , 5 ] devices, continue to inherit two major problems, namely poor stability and low luminance efficiency [ 6 , 7 ]. The main reason for the former lies on photo-oxidation, while the latter is closely associated with low charge carrier mobility and high-energy barrier for its injection.…”