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Abstract The optical scattering properties of porous polyimide (PI) films were investigated for the light-extraction layer in organic light-emitting diodes (OLEDs). By adjusting mixing ratios of different non-solvents during the immersion precipitation process, the light scattering at the generated porous PIs can be precisely tuned. Analyzed from the final OLED devices based on prepared scattering substrates, we found that the light-output characteristics of fabricated devices are correlated with the optical scattering properties, which depends on both the size of generated pores inside porous PIs and the surface roughness at the air-interface. From the help of Mie scattering and Surface scattering simulations, a systematic approach has been performed to explain the influence of the generated micro-structure on both the optical scattering and OLED-performance. Graphical abstract Image 1 Highlights • Porous light-extraction layers for OLEDs with coated polyimides by immersion precipitation. • Fine control of optical scattering properties through tuning mixing ratios of two non-solvents. • Tuning capabilities of light-outcoupling efficiency and angular emission property in OLEDs. • Systematic approach to correlate optical scattering of porous films with OLED performance. • Analysis of influences of the pore-structures using both Mie scattering and surface scattering. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes (OLEDs) currently suffer mostly from only moderate outcoupling efficiencies, calling for many different photonic strategies to increase the share of extracted photons. The quantification of concepts relying on scattering based on periodic or random structures proves complicated and often deserves more attention. To evaluate light extraction methods of OLEDs, we define a procedure leading to a quantifiable extraction efficiency η EE which can be calculated for top- or bottom-emitting OLEDs comprising external as well as internal outcoupling structures. Hence, the extraction efficiency allows to evaluate scattering approaches independently from the employed OLED system. A systematic study of 1D periodically corrugated red top-emitting OLEDs reveals the origin of a moderate enhancement due to an extraction efficiency of η EE  = 14 %. Furthermore, our work provides recommendations how OLEDs with periodic corrugations should be characterized. [ABSTRACT FROM AUTHOR]

We demonstrate an upscalable approach to increase outcoupling in organic light-emitting diodes (OLEDs) fabricated on flexible substrates. The outcoupling enhancement is enabled by introducing a thin film of microporous polyimide on the backside of silver nanowire (AgNW) electrodes embedded in neat colorless polyimide. This porous polyimide film, prepared by immersion precipitation, utilizes a large index contrast between the polyimide host and randomly distributed air voids, resulting in broadband haze (>75%). In addition, the composite polyimide/AgNW scattering substrate inherits the high thermal (>360 °C), chemical, and mechanical stability of polyimides. The outcoupling efficiency of the composite scattering substrate is studied via optical characterization of the composite substrate and electron microscopy of the scattering film. The flexible scattering substrates compared to glass/indium tin oxide (ITO) allows for a 74% enhancement in external quantum efficiency (EQE) for a phosphorescent green OLED, and 68% EQE enhancement for a phosphorescent white OLED. The outcoupling enhancement remains unharmed after 5000 bending cycles at a 2 mm bending radius. Moreover, the color uniformity over viewing angles is improved, an important feature for lighting applications. [ABSTRACT FROM AUTHOR]

We report on the development and detailed investigation of green phosphorescent organic light-emitting diodes (OLEDs) with porous light-scattering layers prepared by combining a simple coating of polyimide-precursor and the immersion precipitation method. With the proper choice of solvent/non-solvent system in the pore-generation process, an external quantum efficiency ( EQE ) of 30.8% and a power efficiency ( PE ) of 82.2 lm/W can be realized at a luminance of 1000 cd/m 2 . By analyzing the angular characteristics in terms of the luminance- and color-variation of OLEDs fabricated with various porous films, we find that the device performance is closely linked to both the light scattering from the porosity and the ray-path change, which depends on the pore shape. Raytracing optical simulation was also used to confirm that the shape-control of the pores in a porous polymer film modulates the light-outcoupling efficiency in OLEDs. [ABSTRACT FROM AUTHOR]

This work presents the possibility of the hollow core nanoparticles to improve luminance in an organic light emitting diode device. The finite difference time domain simulation estimates the effect of the hollow core nanoparticles on the external quantum efficiency of the organic light emitting diode device. The efficiency depends on the size and the volume fraction of the hollow core nanoparticles in the polymer layer, together with the refractive index and the thickness of the polymer layer. It is shown that the hollow core nanoparticles dispersed in a polymer layer can enhance the external quantum efficiency by a factor of 2.5. This work also introduces a continuous production method of the hollow core nanoparticles by using the microfluidic self-assembly of amphiphilic polymers and the layer formation dispersed with them for the rigorous light scattering. [ABSTRACT FROM AUTHOR]

Scattering particles find application in organic light emitting diodes (OLEDs) for an enhanced outcoupling of the generated light. This paper presents a computational scheme to exactly model the electromagnetic fields and the power outcoupling efficiency of a typical OLED geometry, comprising a thin film system with spherical scattering particles inside. The model is based on the expansion of the fields in plane and spherical vector wave functions, as well as the scattering matrix formalism for the layer system reflections. In a numerical application example, the effect of 1000 spherical high index scattering particles on the internal outcoupling from a realistic OLED structure is discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Phosphorescent TrOLEDs have perforated WO3 layer to enhance outcoupling efficiency. [•] Nanostructured TrOLEDs have higher EQE values compared to the conventional TrOLEDs. [•] The values were 28% and 33% higher for bottom and top emission, respectively. [•] The extraction of trapped surface plasmon mode was the main reason for enhancement. [•] The nanostructured TrOLEDs showed optical clarity without haziness. [Copyright &y& Elsevier]

Abstract: We demonstrate a method to increase the efficiency of white organic light emitting diodes (WOLEDs) by a factor of up to 3.7. By fabricating the WOLED on top of a monolayer of SiO2-microspheres we texture the WOLEDs spherically. We attribute the significant increase of the device efficiency to a larger area on the same footprint and to an enhanced outcoupling of waveguide and substrate modes. Measurements reveal that the I–V characteristic of the device as well as the emissive characteristic remains unchanged. [Copyright &y& Elsevier]