Optical Outcoupling Efficiency of Organic Light-Emitting Diodes with a Broad Recombination Profile

Although a broadened recombination zone is beneficial for the lifetime of organic light-emitting diodes (OLEDs), its effect on the optical outcoupling efficiency is unknown. Here, a numerical model to simulate the fraction of photons coupled to air for devices with a broad recombination zone is presented. It is demonstrated that the total outcoupling can be calculated as the integral of the outcoupling efficiency over different positions of emitting dipoles, weighted by the sum-normalized recombination profile, as obtained from electrical modeling. Using single-layer OLEDs based on the thermally delayed activated fluorescence emitter 9,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-9,10-diboraanthracene (CzDBA) as a model system, it is demonstrated that an outcoupling efficiency to the air mode as high as approximate to 26% can be obtained. These simulations are validated with experiments on CzDBA OLEDs of different thickness. The results show that single-layer devices with a broadened emission zone can achieve similar outcoupling efficiency to multilayer OLEDs with an optimized confined emission zone, establishing a route to efficient, stable, and simplified OLEDs.