Simulation strategy for organic LEDs with spectral dissimilarity between photoluminescence and electroluminescence spectra

A red phosphorescent bottom-emitting organic light emitting diode (OLED) comprising host/co-host/dopant system is fabricated using vacuum thermal evaporation method. The measured characteristics of the OLED show a spectral dissimilarity between the photoluminescence and electroluminescence (EL) spectra due to the presence of a shoulder peak in the EL spectrum. This spectral discrepancy is due to the fact that the optical excitation leads mostly to singlet formation while the electrical excitation leads to the formation of both singlets and triplets. The commercial OLED device simulators that are currently available cannot reproduce this shoulder peak in electro-optical simulations. This drawback leads to a mismatch in device efficiency and color coordinates between simulation and experiment. To overcome this problem, a simulation strategy, which involves extraction of the required intrinsic luminescence spectrum for simulation using \({\text {SETFOS}}^{TM}\) ${\text{SETFOS}}^{\mathit{TM}}$ 5.2.8 (Fluxim AG) and peak-deconvolution of the extracted spectrum into Gaussian functions is proposed. By considering a ± 5% variation in refractive indices n of all the layers, the electro-optical simulation results match with that of fabricated red OLED which validates our methodology. The proposed strategy will be helpful for better optimization of such device architecture.