Organic Light‐Emitting Diodes with 30% External Quantum Efficiency Based on a Horizontally Oriented Emitter

Abstract High‐efficiency phosphorescent organic light‐emitting diodes (OLEDs) doped with Ir(ppy) 2 (acac) bis(2‐phenylpyridine)iridium(III)‐acetylacetonate in an exciplex forming co‐host have been optically analyzed. This emitter has a preferred orientation with the horizontal to vertical dipole ratio of 0.77:0.23 as compared to 0.67:0.33 in the isotropic case. Theoretical analysis based on the orientation factor ( Θ , the ratio of the horizontal dipoles to total dipoles) and the photoluminescence quantum yield ( q PL ) of the emitter predicts that the maximum external quantum efficiency (EQE) of the OLEDs with this emitter is about 30%, which matches very well with the experimental data, indicating that the electrical loss of the OLEDs is negligible and the device structure can be utilized as a platform to demonstrate the validity of optical modeling. Based on the results, the maximum EQE achievable for a certain emitting dye in a host can be predicted by just measuring q PL and Θ in a neat film on glass without the need to fabricate devices, which offers a universal plot of the maximum EQE as a function of q PL and Θ .