Organic light-emitting diodes with ultrastable glass emission layers show increased efficiency and device stability.

Hyperbranched polyvinylsulfi des have been prepared through a facile, metal-free, radical induced "A 2 +B 3 " thiol-yne polymerization of 1,3,5-tris(naphthalylethynyl) benzene and 1,4-dithiolbenzene with three different input ratios. The resulting polymers exhibit excellent optical properties like high transparency and very high refractive index (RI) of up to 1.7839, combined with high thermal stability ( T d5% up to 420 °C) and excellent solution processability. These properties make them ideal candidates as high RI polymeric materials (HRIP) in connection with light out-coupling schemes for organic light-emitting diodes (OLEDs). A series of hyperbranched HRIPs with varying monomer compositions have been compared in their optical properties. Finally, phosphorescent monochrome OLEDs are fabricated on top of HRIP layers to test the compatibility of HRIPs with state-of-the-art OLEDs. The results show that the HRIPs do not deteriorate the performance of the OLEDs while maintaining external quantum effi ciencies of over 20% for phosphorescent red OLEDs. These results open a pathway toward alternative, low-cost, and scalable out-coupling concepts through refractive index matching of the OLED materials and the HRIPs presented.

Organic light-emitting diodes (OLEDs) suffer from notorious light trapping, resulting in only moderate external quantum efficiencies. Here, we report a facile, scalable, lithography-free method to generate controllable nanostructures with directional randomness and dimensional order, significantly boosting the efficiency of white OLEDs. Mechanical deformations form on the surface of poly(dimethylsiloxane) in response to compressive stress release, initialized by reactive ions etching with periodicity and depth distribution ranging from dozens of nanometers to micrometers. We demonstrate the possibility of independently tuning the average depth and the dominant periodicity. Integrating these nanostructures into a two-unit tandem white organic light-emitting diode, a maximum external quantum efficiency of 76.3% and a luminous efficacy of 95.7 lm W −1 are achieved with extracted substrate modes. The enhancement factor of 1.53 ± 0.12 at 10,000 cd m −2 is obtained. An optical model is built by considering the dipole orientation, emitting wavelength, and the dipole position on the sinusoidal nanotexture.

We demonstrate enhanced light extraction for monochrome top-emitting organic light-emitting diodes (OLEDs). The enhancement by a factor of 1.2 compared to a reference sample is caused by the use of a hole transport layer (HTL) material possessing a low refractive index (∼ 1.52). The low refractive index reduces the in-plane wave vector of the surface plasmon polariton (SPP) excited at the interface between the bottom opaque metallic electrode (anode) and the HTL. The shift of the SPP dispersion relation decreases the power dissipated into lost evanescent excitations and thus increases the outcoupling efficiency, although the SPP remains constant in intensity. The proposed method is suitable for emitter materials owning isotropic orientation of the transition dipole moments as well as anisotropic, preferentially horizontal orientation, resulting in comparable enhancement factors. Furthermore, for sufficiently low refractive indices of the HTL material, the SPP can be modeled as a propagating plane wave within other organic materials in the optical microcavity. Thus, by applying further extraction methods, such as micro lenses or Bragg gratings, it would become feasible to obtain even higher enhancements of the light extraction.

Single-carrier devices are an excellent model system to study charge injection and charge transport properties of (doped) transport layers and to draw conclusions about organic electronics devices in which they are used. By combining steady-state and impedance measurements at varying temperatures of hole-only devices with different intrinsic layer thicknesses, we are able to determine all relevant material parameters, such as the charge mobility and the injection barrier. Furthermore, the correlation and sensitivity analyses reveal that the proposed approach to study these devices is especially well suited to extract the effective doping density, a parameter which cannot be easily determined otherwise. The effective doping density is crucial in organic light-emitting diodes (OLEDs) for realizing efficient injection, charge balance, and lateral conductivity in display or lighting applications. With the fitted drift-diffusion device model, we are further able to explain the extraordinary two-plateau capacitance–frequency curve of these hole-only devices, which originates from charges that flow into the intrinsic layer at zero applied offset voltage. We demonstrate that the observation of this behaviour is a direct indication for ideal charge injection properties and the observed capacitance–frequency feature is linked to the charge carrier mobility in the intrinsic layer. The extracted material parameters may directly be used to simulate and optimize full OLED devices employing the investigated hole-injection and -transport materials.