ИСТИНА

One of the main problems in modern organic light-emitting diodes (OLEDs), especially in blue ones, is their insufficient lifetime in the operating conditions. One of the key reasons of OLEDs degradation is associated with the degradation of the organic emissive layers and their interfaces mainly within the electron-hole recombination zone, where the exciton density is high. As a result, the energy density is high as well, which can result in a high probability of degradation. The spatial profile of the recombination rate within the recombination zone is determined by mobilities of charge carriers, relative permittivity, as well as the misalignment of the HOMO and LUMO levels of the two materials at the interface of adjacent layers. In this work, using numerical modeling based on the drift-diffusion model, the dependence of the spatial distribution of the recombination rate of charge carriers on their mobilities has been revealed (Figure 1). Figure 1c shows, that at high charge carrier mobility in the active layer (~10–2 cm2/V·s), charge recombination regions are localized near the interfaces of the emissive layer with charge transport layers. At the lower charge mobilities in the active layer (~10–5 cm2/V·s), a bell-shaped spatial dependence of the recombination rate is observed (Figure 1b). Сonsequently, the recombination area is distributed over the entire emission layer, and this should be benefitial for a long OLED lifetime. Unexpectedly, the high charge mobilities in the active layer could be a factor shortining the OLED lifetime. These findings can provide guidelines for improving the stability of OLEDs. This work was supported by Russian Science Foundation (project № 24-49-02038).