Multispectral surface plasmon resonance approach for ultra-thin silver layer characterization: Application to top-emitting OLED cathode

Abstract

While dielectric/metal/dielectric (DMD) multilayer thin films have raised considerable interest as transparent and conductive electrodes in various optoelectronic devices, the knowledge of optical characteristics of thin metallic layers integrated in such structures is still rather approximate. The multispectral surface plasmon resonance characterization approach described in this work precisely aims at providing a rigorous methodology able to accurately determine the optical constants of ultra-thin metallic films. As a practical example, the refractive index and extinction dispersion curves of 8 to 25 nm-thick silver layers have been investigated. As a result, their extreme dependence on the layer thickness is highlighted, in particular in a thickness range close to the critical threshold value (∼10 nm) where the silver film becomes continuous and its electrical conductance/optical transmittance ratio particularly interesting. To check the validity of the revisited Ag layers constant dispersion curves deduced from this study, they were introduced into a commercial optical model software to simulate the behavior of various optoelectronic building blocks from the simplest ones (DMD electrodes) to much more complex structures [full organic light emitting device (OLED) stacks]. As a result, a much better prediction of the emission spectrum profile as well as the angular emission pattern of top-emitting OLEDs is obtained. On this basis, it is also shown how a redesign of the top encapsulation thin film of OLEDs is necessary to better take benefit from the advanced DMD electrode. These results should particularly interest the micro-OLED display field where bright and directive single color pixel emission is required.

Effects of Insertion of Ag Mid-Layers on Laser Direct Ablation of Transparent Conductive ITO/Ag/ITO Multilayers: Role of Effective Absorption and Focusing of Photothermal Energy

“…For Ag mid-layer thicknesses of 6, 13, and 16 nm, the threshold laser beam fluence were 0.39, 0.28, and 0.27 J/cm2, respectivel lower ablation thresholds of the ITO/Ag/ITO MLs were attributed to conductivity and absorption coefficient of the inserted Ag mid-layer the ablation threshold of the ITO/Ag/ITO MLs reduced slightly as Ag t Figure 5 shows the SEM images of the spot-shaped laser-ablated patterns on ITO/Ag/ITO MLs with different Ag thicknesses at a fixed scanning speed of 2000 mm/s and a laser pulse energy of 97 μJ. The spot patterns were generated by the overlapping rate, i.e., the scanning speed of the laser beam divided by the repetition rate of the laser beam [20]. At a lower repetition rate, a higher laser pulse beam energy was obtained at the same scanning speed.…”

“…However, replacing the metal electrodes with pure TCOs in large-sized FPDs or TSPs is not optimal because of their lower conductivities compared with those of metals. Therefore, various oxide–metal–oxide (OMO) multilayers (MLs) have been considered and investigated as candidate replacements exhibiting of both high optical transparency and electrical conductivity [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Despite the insertion of thin metal mid-layers between TCO films, the transparency of OMO MLs did not reduce significantly, whereas the electrical conductivities improved compared with those of pure TCO [ 23 , 24 , 25 ].…”

Realizing 8 cd A−1 Current Efficiency for Solution-Processed Inverted Top-Emitting Polymer Light-Emitting Diodes

“…TOLEDs show a high aperture ratio in active-matrix displays as the activematrix circuit is located at the bottom of the device. Any type of substrate can be used for TOLEDs as it does not need to be transparent, for example silicon wafer, 1 paper, 2 or clothing. 3 Transparent conducting oxides such as indium tin oxide (ITO) 4,5 and indium zinc oxide (IZO) 6 can be sputtered as a top electrode by firstly protecting the organic layers to not damage them.…”

“…25,26 However, it is more difficult to precisely control the organic layer thicknesses. Therefore, only a few studies have been conducted to develop TOLEDs by solution process, [27][28][29][30][31] while microcavity TOLEDs fabricated by thermal evaporation have been widely studied 1,6,16,32 Chien et al fabricated a green inverted TOLED with a solution-processed top electrode based on transparent carbon nanotubes and solution-processed emissive and hole injection (HIL) layers. 27 They reported a current efficiency of 1.24 cd A À1 without microcavity effects due to high transmittance of the top electrode, showing the feasibility of large-scale solution-processed TOLEDs.…”

Ultrathin sputter-deposited plasmonic silver nanostructures

“…The optical properties of ultrathin Ag lms can vary strongly from bulk optical properties. 12,13 The reason for deviations is commonly found to be the noncontinuity of the metal and therefore the excitation of localized surface plasmon resonances that occur at grains or in voids. In addition, surface roughness of otherwise continuous lms is suggested to alter the optical properties of thin lms, 14,15 as the surface scattering of conduction electrons leads to increased losses compared to the bulk.…”