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A method for treating current and voltage excitation of organic light-emitting diodes in the context of drift-diffusion models is discussed. Findings reveal an exponential rise in conduction current and a linear rise in the voltage.

Numerical simulations were used for examining the impact of charge carrier and triplet-exciton absorption on the threshold current density of an organic double-heterostructure (DH) laser diode structure. Findings revealed no significant reduction in polaron absorption due to an increase in charge carrier mobility in the transport layers.

A comprehensive investigation of the influence of various parameters on the model gain and laser threshold power density in electrically pumped single-layer organic semiconductor structures is presented. The electric model can be applied to organic light-emitting diodes (OLEDs) and the results also serve as a guideline for the design and optimization of future devices.

We examine the impact of various annihilation processes on the laser threshold current density of a multilayer organic laser diode by numerical simulation. Our self-consistent numerical model treats the dynamics of electrons, holes, and singlet as well as triplet excitons in the framework of a drift-diffusion model. The resulting particle distributions enter into an optical model. In our approach, a three layer waveguide structure is taken into account and the resulting laser rate equations are solved. Various annihilation processes are included as reactions between the different particle species in the device employing typical annihilation rates and material properties of organic semiconductors. By systematically varying the device dimensions and the annihilation rate coefficients, the dominating quenching processes are identified. The threshold current density is found to depend sensitively on the thickness of the emission layer. The influence of annihilation processes on the threshold current density is quantified as a function of the emission layer thickness and various annihilation rate coefficients. Using typical annihilation rate coefficients singlet-polaron annihilation is found to be the dominating quenching process. Maximum annihilation rate coefficients are calculated allowing a threshold current density below 1 kA/cm2. Singlet-triplet annihilation is recognized as another main loss process for singlet excitons. In our model the singlet exciton density is increased by triplet-triplet annihilation whereas it is diminished by singlet-triplet annihilation. The ratio of the rate coefficients for singlet-triplet and triplet-triplet annihilations is identified to be critical for the total number of singlet excitons being quenched by triplet excitons. [ABSTRACT FROM AUTHOR]

Our former findings on the charge balance in blue fluorescent devices show a clear connection between the basic performance parameters: Efficiency and lifetime both show an optimum with respect to voltage. Unfortunately, for devices using a conventional hole injection and NPB as hole transport material, the optimum values do not occur at the same voltage. Moreover, the optimum voltage for lifetime is much higher than that for optimum efficiency. After investigating the underlying charge balance issues, we developed new stack layouts and hole transport materials to shift the lifetime optimum to lower voltage values. Using an appropriate hole injection layer and one of our latest hole transport materials, we can now combine excellent lifetime, low voltage and good efficiency in one fluorescent blue device. In addition, we obtain 10% EQE by carefully tuning the hole transport side in fluorescent blue devices. No special hole blocking layer is required to obtain this high efficiency. For green phosphorescent devices, we developed a thermally stable co-host material which allows for the use of low emitter concentrations in the range of 5% without sacrificing device performance. We combine this material with an electron transporting host that shows a slight initial rise in lifetime when a low emitter concentration is employed. Due to these features, the tuning of the host mixing ratio results in excellent LT95 values in combination with good voltage, efficiency and low efficiency rolloff for high luminance. [ABSTRACT FROM AUTHOR]

Specifically in large size OLED display applications the use of strong cavity tuning to achieve deep blue coordinates has a negative impact on the device viewing angle from both a luminance and colour shift as well as cost perspective. Here we report on materials which achieve CIE colours below y = 0.07 and a high lifetime. [ABSTRACT FROM AUTHOR]