Analysis of the efficiency performance of different bilayered triplet-triplet fusion OLEDs with carriers and exciton simulations

In this work, the exciton diffusion model coupled with a drift-diffusion solver is used to simulate three bilayer TTF-OLEDs devices, which triplet tank layer (TTL) is DMPPP (Device A), DCPPP (Device B), and PPC (Device C), respectively. The simulation results are matched to the experimental data, and the efficiency and loss mechanisms are studied. The main reason for IQE loss is triplet-polaron quenching (TPQ) and the ability of triplet diffusion. The experimental result of the device has a recorded 15.5% efficiency in TTF OLEDs, which are benefitted due to the high diffusion coefficient and fewer electrons accumulated in the converting layer to avoid the TPQ processes. This is due to the LUMO of PPC being matched to the second layer to avoid carrier accumulation at the interface. Device A has a good diffusion ability and low TPQ coefficients but suffers from electron accumulation at the interfaces. The worst case (B) has a low diffusion coefficient with a high TPQ coefficient, which has a weak triplet density in the NPAN layer to induce the TTF processes. Besides the bilayer studies, the single-layer structures are also studied to extract some key parameters for bilayer studies. It is interesting to find that material with high TPQ coefficients can quench the triplets to stop the triplet-singlet annihilation, which will have a higher efficiency in the single-layer material. However, it plays the opposite role in bilayer structures because triplets are quenched before they reach the NAPA layers.