In this work, the emission efficiency and spectral shift with respect to viewing angle were optimized by optimizing the
design of the multi-layer top mirror of a microcavity OLED device. We first established criteria for the emission side
mirror in order to optimize light intensity and spectral shift with viewing angle. Then we designed mirror using metallic
and dielectric layers based on the target defined. The electroluminescence emission spectra of a microcavity OLED
consisting of widely used organic materials, N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole
transport layer and tris (8-hydroxyquinoline) (Alq3) as emitting and electron transporting layer was then calculated.
Silver was used as the anode and back reflection mirror for the microcavity OLED. The simulation was performed for
both the conventional LiF/Al cathode/top mirror and the optimized 5-layered top mirror. Our results indicate that by
following the design procedure outlined, we simultaneously optimize the device for better light intensity and spectral
shift with viewing angle.
We report on detailed simulations of the emission from microcavity OLEDs consisting of widely used organic materials, N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq3) as emitting and electron transporting layer. The thick silver film was considered as a top mirror, while silver or copper films on quartz substrate were considered as bottom mirrors. The electroluminescence emission spectra, electric field distribution inside the device, carrier density and recombination rate were calculated as a function of the position of the emission layer, i.e. interface between NPB and Alq3. In order to achieve optimum emission from a microcavity OLED, it is necessary to align the position of the recombination region with the antinode of the standing wave inside the cavity. Once the optimum structure has been determined, the microcavity OLED devices were fabricated and characterized. The
experimental results have been compared to the simulations and the influence of the emission region width and position on the performance of microcavity OLEDs was discussed.
This work reports on simulation and experimental investigation into the charge transport and electroluminescence in a quantum well (QW) organic light emitting diode (OLED) consisting of a N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole transport layer, tris (8-hydroxyquinoline) aluminum (Alq3) as a potential barrier and electron transporting layer, and rubrene as potential well layer. Indium tin oxide was used as an anode, while LiF/Al was employed as a cathode. The carrier transport was simulated using one-dimensional time-independent drift-diffusion model. The influence of the well width, barrier width, and the number of QWs on the carrier distribution, recombination rate, and device performance was investigated. Finally, the device structures which yielded most promising simulation results were fabricated and characterized. The comparison between the experimental and theoretical results is discussed.
In this work we present detailed analysis of the emitted radiation spectrum from tris(8-hydroxyquinoline) aluminum (Alq3) based OLEDs as a function of: the choice of cathode, the thickness of organic layers, and the position of the hole transport layer/Alq3 interface. The calculations fully take into account dispersion in glass substrate, indium tin oxide anode, and in the organic layers, as well as the dispersion in the metal cathode. Influence of the incoherent transparent substrate (1 mm glass substrate) is also fully accounted for. Four cathode structures have been considered: Mg/Ag, Ca/Ag, LiF/Al, and Ag. For the hole transport layer, N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) was considered. As expected, emitted radiation is strongly dependent on the position of the emissive layer inside the cavity and its distance from the metal cathode. Although our optical model for an OLED does not explicitly include exciton quenching in vicinity of the metal cathode, designs placing emissive layer near the cathode are excluded to avoid unrealistic results. Guidelines for designing devices with optimum emission efficiency are presented. Finally, the optimized devices were fabricated and characterized and experimental and calculated emission spectra were compared.