In this paper, numerical algorithms for extraction of optoelectronic material and device parameters in organic light-emitting devices (OLEDs) are presented and tested for their practical use. Of particular interest is the extraction of the emission profile and the source spectrum. A linear and a nonlinear fitting method are presented and applied to emission spectra from OLEDs in order to determine the shape of the emission profile and source spectrum. The motivation of the work is that despite the existence of advanced numerical models for optical and electronic simulation of OLEDs, their practical use is limited if methods for the extraction of model parameters are not well established. Two fitting methods are presented and compared to each other and validated on the basis of consistency checks. Our investigations show the impact of the algorithms on the analysis of realistic OLED structures. It is shown that both fitting methods p form reasonably well, even if the emission spectra to be analyzed are noisy. In some cases the nonlinear method performs slightly better and can achieve a perfect resolution of the emission profile. However, the linear method provides the advantage that no assumption on the mathematical shape of the emission profile has to be made.
Advanced Numerical Simulation of Organic Light-emitting Devices
21www.intechopen.com organic semiconductors. The disordered nature of organic semiconductors affects the density of state, the mobility model, the Einstein diffusion relation as well as charge injection. These novel physical model ingredients constitute a second generation OLED model and are implemented in the simulator SETFOS (Fluxim AG, 2010). It is expected that the second generation OLED model will impact the way OLED characteristics and performance are quantitatively described.
Description of the device model 2.1 Charge drift-diffusion modelTo describe the main features of charge transport in organic LEDs four processes have to be considered as illustrated in the schematic energy level diagram in Fig. 1. In a first step, charge carriers have to be injected into the organic material (1), secondly they will be transported (2) until they recombine to an exciton (3). Then the excitons decay radiatively or non-radiatively (4). In the following we will first look at the transport process (2). For the description of the electrical potential ψ is related to the mobile electron and hole densities n and p and the trapped electron and hole densities n t and p t where e is the elementary charge and ǫ the product of the vacuum permittivity ǫ 0 and the relative permittivity ǫ r of the organic material. The current equations for electrons and holes read J n = −enμ n ∇ψ + eD n ∇n, J p = −epμ p ∇ψ − eD p ∇p (2)
434Optoelectronic Devices and Properties
Abstract. We demonstrate the importance of a comprehensive modeling of the dynamics of excited states in organic optoelectronics devices. Our numerical analysis demonstrates that exciton distributions extracted from spectral emission measurements of OLEDs are equivalent to those obtained by solving charge and exciton transport equations when the position-dependent coupling to optical modes is taken into account. The transport simulations are based on the extended Gaussian disorder model for organic semiconductors. Further, we show that the same numerical modeling framework can be used to accurately simulate bulk-heterojunction organic solar cells with dissociation of charge-transfer excitons. The simulations are compared to experimental data. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).
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