Abstract:Light emission by excited species that decay via an electrical dipole transition is
modeled as an electrical dipole antenna. We examine the various effects that
occur when such a dipole is close to a metallic interface: wide-angle interference,
coupling to the surface plasmon mode and absorption of the near-field. Analytical
expressions for the power coupled to the surface plasmon and near-field absorption are
derived. The case of a non-absorbing metal is compared to that of an absorbing
metal.
“…1a). This causes plasmon-mediated losses especially for perpendicular emitters 18 , resulting in a reduced lifetime compared to parallel emitters due to orientation dependent Purcell factors.Figure 1The geometry of the two OLED types ( a ) is shown with an illustration of the orientation averaging models ( b , c , d ) and the corresponding expected transient observation ( e , f , g ). In ( a ) the emission patterns generated by the three orthogonal dipoles are plotted for the d = 30 nm case inside the substrate (angle θ s with respect to the normal, accessed experimentally by half ball lens coupling) or in air (angle θ A ).…”
Section: Introductionmentioning
confidence: 99%
“…1a ). This causes plasmon-mediated losses especially for perpendicular emitters 18 , resulting in a reduced lifetime compared to parallel emitters due to orientation dependent Purcell factors. Figure 1 The geometry of the two OLED types ( a ) is shown with an illustration of the orientation averaging models ( b , c , d ) and the corresponding expected transient observation ( e , f , g ).…”
The non-isotropic alignment of molecules can increase the interaction efficiency with propagating light fields. This applies to both emissive and absorptive systems and can be exploited for achieving unprecedented efficiencies of organic opto-electronic devices such as organic light-emitting diodes. Optical analysis has revealed certain phosphorescent emitters to align spontaneously in an advantageous orientation. Unfortunately, established approaches only determine an average orientation because emission patterns solely depend on the second moments of the transition dipole vector distribution. In order to resolve further details of such a distribution, additional differences in the emission characteristics of parallel and perpendicularly oriented emitters need to be introduced. A thin metal layer near the emitters introduces plasmon mediated losses mostly for perpendicular emitters. Then, analyzing the emission at different polarizations allows one to measure emission lifetimes of mostly parallel or mostly perpendicular oriented emitters. This should alter the transient emission when observing the temporal phosphorescence decay under different directions and/or polarizations. The angular width of the orientation distribution can be derived from the degree of such lifetime splitting. Our results suggest a narrow but obliquely oriented molecular ensemble of Ir(MDQ)2(acac) doped into the α-NPD host inside an Organic LED stack.
“…1a). This causes plasmon-mediated losses especially for perpendicular emitters 18 , resulting in a reduced lifetime compared to parallel emitters due to orientation dependent Purcell factors.Figure 1The geometry of the two OLED types ( a ) is shown with an illustration of the orientation averaging models ( b , c , d ) and the corresponding expected transient observation ( e , f , g ). In ( a ) the emission patterns generated by the three orthogonal dipoles are plotted for the d = 30 nm case inside the substrate (angle θ s with respect to the normal, accessed experimentally by half ball lens coupling) or in air (angle θ A ).…”
Section: Introductionmentioning
confidence: 99%
“…1a ). This causes plasmon-mediated losses especially for perpendicular emitters 18 , resulting in a reduced lifetime compared to parallel emitters due to orientation dependent Purcell factors. Figure 1 The geometry of the two OLED types ( a ) is shown with an illustration of the orientation averaging models ( b , c , d ) and the corresponding expected transient observation ( e , f , g ).…”
The non-isotropic alignment of molecules can increase the interaction efficiency with propagating light fields. This applies to both emissive and absorptive systems and can be exploited for achieving unprecedented efficiencies of organic opto-electronic devices such as organic light-emitting diodes. Optical analysis has revealed certain phosphorescent emitters to align spontaneously in an advantageous orientation. Unfortunately, established approaches only determine an average orientation because emission patterns solely depend on the second moments of the transition dipole vector distribution. In order to resolve further details of such a distribution, additional differences in the emission characteristics of parallel and perpendicularly oriented emitters need to be introduced. A thin metal layer near the emitters introduces plasmon mediated losses mostly for perpendicular emitters. Then, analyzing the emission at different polarizations allows one to measure emission lifetimes of mostly parallel or mostly perpendicular oriented emitters. This should alter the transient emission when observing the temporal phosphorescence decay under different directions and/or polarizations. The angular width of the orientation distribution can be derived from the degree of such lifetime splitting. Our results suggest a narrow but obliquely oriented molecular ensemble of Ir(MDQ)2(acac) doped into the α-NPD host inside an Organic LED stack.
“…The distance between the emitter and the Al layer was set at 80nm, which showed the best If we compare this enhancement to a bottom emitting OLED, we sse that a TOLED has an enhanced outcoupling by a factor 1.68 and a bottom emitting OLED has an enhanced outcoupling of 1.40 (in substrate and air). This is because in a TOLED the interference effects and plasmon coupling is stronger.Using only horizontal dipoles results in better tuning of the interference effects (because vertical and horizontal dipoles have different phases) and reduced plasmon coupling [9]. This has a comparitively larger effect in a TOLED.…”
Recently preferential orientation was demonstrated in phosphorescent emitters. We simulate the efficiency of oriented emitters in bottom and top-emitting OLEDs. The oucoupling is increased by a factor 1.4 and 1.68 for bottom and top emission.
“…For modeling of these two effects we use an ensemble of incoherent electrical dipole antennas with random orientation, 6,7 used in earlier work. [8][9][10][11] It is assumed that the OLED is a one-dimensional layer structure since its lateral dimensions (>1 mm) are much larger than its thickness ($1 lm). The emission of the dipole antenna is decomposed in plane and evanescent coherent waves with a transverse electric (TE) and transverse magnetic (TM) polarization.…”
Section: A External Quantum Efficiency (Eqe)mentioning
confidence: 99%
“…The radiative efficiency g rad of an emitting organic material is directly related to the exciton decay time s. It is well known 3,10,12 that the exciton decay time depends on the optical environment (the layer thicknesses and refractive indices of the materials in the OLED) which is equivalent to the Purcell effect. 13 Therefore, g rad also depends on the optical environment.…”
Section: A External Quantum Efficiency (Eqe)mentioning
One of the most important parameters of organic light-emitting devices (OLEDs) in their application for illumination or displays is their efficiency. In order to maximize the efficiency, one needs to understand all loss mechanisms and effects present in these devices and properly model them. For that purpose, we introduce an integrated model for light emission from OLEDs. The model takes into account the exciton decay time change and light outcoupling. Furthermore, it shows how to calculate the external quantum efficiency, the spectral radiance and the luminous current efficacy of OLEDs. The overall theory is experimentally verified through a range of measurements done on a set of green OLED samples with an Ir-based phosphorescent emitter. From the analysis of simulations and experiments one can estimate the charge balance in the OLED stack and the radiative efficiency of the emitter.
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