In multilayer white organic light-emitting diodes the electronic processes in the various layers--injection and motion of charges as well as generation, diffusion and radiative decay of excitons--should be concerted such that efficient, stable and colour-balanced electroluminescence can occur. Here we show that it is feasible to carry out Monte Carlo simulations including all of these molecular-scale processes for a hybrid multilayer organic light-emitting diode combining red and green phosphorescent layers with a blue fluorescent layer. The simulated current density and emission profile are shown to agree well with experiment. The experimental emission profile was obtained with nanometre resolution from the measured angle- and polarization-dependent emission spectra. The simulations elucidate the crucial role of exciton transfer from green to red and the efficiency loss due to excitons generated in the interlayer between the green and blue layers. The perpendicular and lateral confinement of the exciton generation to regions of molecular-scale dimensions revealed by this study demonstrate the necessity of molecular-scale instead of conventional continuum simulation.

Despite the poor screening of the Coulomb potential in organic semiconductors, excitons can dissociate efficiently into free charges at a donor–acceptor heterojunction, leading to application in organic solar cells. A kinetic Monte Carlo model that explains this high efficiency as a two‐step process is presented. Driven by the band offset between donor and acceptor, one of the carriers first hops across the interface, forming a charge transfer (CT) complex. Since the electron and hole forming the CT complex have typically not relaxed within the disorder‐broadened density of states (DOS), their remaining binding energy can be overcome by further relaxation in the DOS. The model only contains parameters that are determined from independent measurements and predicts dissociation yields in excess of 90% for a prototypical heterojunction. Field, temperature, and band offset dependencies are investigated and found to be in agreement with earlier experiments. Whereas the investigated heterojunctions have substantial energy losses associated with the dissociation process, these results suggest that it is possible to reach high dissociation yields at low energy loss.

wileyonlinelibrary.comand excitonic processes and determining the values of the relevant material-specifi c parameters, ii) supporting the layer stack design process by providing an effi cient route for developing understanding of the benefi ts and disadvantages of the use of novel materials and layer stack concepts. The third (vertical) axis in the fi gure indicates examples of the performance characteristics which may be studied using the simulations. We envisage that simulations can be used to clarify the sensitivity of the OLED device performance to materials and layer stack parameters, and can provide insights in the functioning of OLEDs beyond the capability of experiments. For example by a much more precise control of the device structure, by providing insight in all processes at an ultimate (molecular-scale) spatial resolution and at the shortest relevant time scales, and by providing the opportunity to explore the performance under conditions which are experimentally not realizable. A long-term goal of our research is therefore to develop and apply a simulation method which can address any combination of the three application types, and which provides a platform within which novel insights as obtained in each of the fi elds indicated in the fi gure can be readily adopted.So far, commonly used OLED simulations methods are based on one-dimensional drift-diffusion approaches (see Coehoorn and Bobbert and references therein) [ 2 ] in which the charge transport and excitonic processes are included in a semi-empirical manner. However, it is well-known that as a result of the energetic disorder, resulting from the structural disorder, the current density in OLEDs is fi lamentary, rather than uniform. [ 3 ] We have shown from molecular-scale three-dimensional kinetic Monte Carlo (3D-KMC) modelling that, as a consequence, the emission takes place on certain preferred molecular sites, rather than being laterally uniform. [ 4 ] It is thus necessary to develop a full 3D-KMC model for accurately simulating the effect of the loss processes, such as triplet-polaron quenching and triplet-triplet annihilation in phosphorescent OLEDs. These losses lead to an effi ciency decrease with increasing current density and luminance (roll-off of the internal quantum effi ciency, η IQE ). We have recently extended the 3D-KMC method to include the charge transport and all excitonic processes in an integral manner. [ 5 ] The simulations were found to provide a good description of the roll-off of archetypical green and red emitting OLEDs studied intensively in the literature, [ 6 ] and were used to The performance of organic light-emitting diodes (OLEDs) is determined by a complex interplay of the optoelectronic processes in the active layer stack. In order to enable simulation-assisted layer stack development, a threedimensional kinetic Monte Carlo OLED simulation method which includes the charge transport and all excitonic processes is developed. In this paper, the results are presented of simulations including degradation processes...