Influence of the 1,2,4-linking hyperbranched poly(arylenevinylene) structure on organic light emitting diode performance as compared to conventional 1,3,5-linking one

Abstract

The influence of a novel 1,2,4-linking hyperbranched poly(arylenevinylene) (1,2,4-hb-PAV) material, designed to feature intramolecular energy-funneling, on the transport and emission properties of organic light emitting diodes (OLEDs) has been studied. A comparison to conventional hyperbranched 1,3,5-linking polymers (1,3,5-hb-PAV), which do not exhibit this effect, has been made. For this purpose, single-layer organic light emitting diodes with a glass/indium–tin oxide/poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate)/active layer/Ca/Al structure and different active layer thicknesses have been fabricated and characterized, using either 1,2,4-hb-PAV or 1,3,5-hb-PAV as active layers. The current–voltage response has been interpreted in terms of a numerical model that includes a field-dependent carrier mobility, which allows us to estimate carrier mobility in the diodes. Stable green emission with Commission Internationale de L’Eclairage coordinates at (0.41,0.56) and a high luminous efficiency of 28 Cd/A has been obtained at very low driving currents (10 μA) for 1,2,4-hb-PAV material, versus 2.1 Cd/A for the conventional 1,3,5-linking material, in spite of the high photoluminescence quantum yield in thin film exhibited by both materials. The significant improvements in the performance of OLEDs based on 1,2,4-hb-PAV with respect to other conventional hyperbranched polymers are attributed to the inherent energy gradient from the shorter branches to the longer conjugated stem in this structure, which enables the characteristic funneling effect.

Charge Transport and Sensitized 1.5 μm Electroluminescence Properties of Full Solution-Processed NIR-OLED based on Novel Er(III) Fluorinated β-Diketonate Ternary Complex

“…In this case, it is more straightforward to derive the inverse function x ( E 0 , E L , J b ), where the integration limits E 0 and E L are the values of the internal electric fields at both contacts: E 0 = E ( x = 0), E L = E ( x = L). Further details of these calculations are given elsewhere. , A second integration of the electric field using eq , provides the electrical response of the diode V b ( E 0 , E L , J b ). The determination of the unknown value E 0 is carried out numerically via the continuity equation for the current density across the device: J inj ( E 0 ) = J b where J inj is the injection current according to a certain injection formulation of the injection process.…”

“…Such a model must include structural characteristics of the device, such as layer thicknesses or active diode area, material parameters such as carrier mobility, μ, and characteristics of interfaces such as potential barriers for carrier injection from the electrodes. The model proposed resolves at the same time space-charge effects, together with injection mechanisms and nonvanishing electric fields at the contact interfaces, , so as to avoid making assumptions – as in previous models in the literature – about the conduction regime (injection-limited or bulk-limited) to extract parameters . To achieve this goal we have used a simple formulation based on the fundamental equations for the drift current (eq ), the 1D Poisson (eq ), and the integral expression of the applied external voltage (eq ) under single-carrier approach: J normalb = e μ ( E ) [ p n ] E ( x ) = e μ 0 .25em exp ( k E false( x false) ) [ p n ] E ( x ) normald E ( x ) normald x = e [ p ] ε ε 0 V b = prefix∫ normalo L E false( x false) d x …”

Highly efficient solution-processed white organic light-emitting diodes based on novel copolymer single layer

“…We use a quasi-Newton algorithm to fit the experimental data, considering 0 and k as the only physical parameters in the classical expression of mobility. Details of the model can be seen elsewhere [14,15]. In view of the energetic level diagram for both materials [4], it is expected that conduction is mainly carried out by electrons.…”

Novel Erbium(III) and Ytterbium(III)-based materials for Optoelectronic and Telecommunication Applications

“…Such a model must include structural characteristics of the device, such as layer thicknesses or active diode area, material parameters such as carrier mobility, μ(E), and characteristics of interfaces such as potential barriers for carrier injection from the electrodes. The model proposed resolves at the same time space charge effects, together with injection mechanisms and non-vanishing electric fields at the contact interfaces [264,265], so as to avoid making assumptions -as in previous models in the literature-on the conduction regime (injection limited or bulk limited) in order to extract parameters [266]. So as to achieve this goal we have used a simple formulation based on the fundamental equations for the drift current (1), the one-dimensional Poisson equation (2 (2)…”

“…Further details of these calculations are given elsewhere [264,265]. A second integration of the electric field using (3), provides the electrical response of the diode V b (E 0 ,E L ,J b ).…”