Efficient, Nonintrusive Outcoupling in Organic Light Emitting Devices Using Embedded Microlens Arrays

Abstract

We demonstrate efficient light extraction from the active region of bottom-emitting organic light emitting devices (OLEDs) using a high refractive index, nondiffractive hemispherical microlens array located between the transparent anode and embedded in the low refractive index glass substrate (n = 1.5). The subelectrode microlens array (SEMLA) results in a maximum external quantum efficiency of 70 ± 4% for green phosphorescent OLEDs (PHOLEDs). Furthermore, the wavelength- and viewing-angle-independent light extraction structure results in white PHOLED external efficiencies of 50 ± 3%. The SEMLA light extraction structure is nonintrusive; that is, it lies completely outside of the OLED structure. Since this design has no effect on the image resolution, it is compatible with applications for both displays and white light illumination, with no dependence on molecular transition dipole orientation and the active organic layers (and hence diode electrical characteristics) used in the PHOLED. Finally, due to the micrometer-scale feature size of the SEMLA, it is achieved using conventional photolithography prior to the OLED array deposition.

Improved Outcoupling Efficiency and Stability of Perovskite Light‐Emitting Diodes using Thin Emitting Layers

“…Consistent with our experimental observations, optimal outcoupling efficiency occurs with perovskite thicknesses in the range of 35–40 nm, where waveguide mode loss is minimized. Furthermore, substrate mode loss is also increased for 35–40 nm thick perovskite emitting layers, which provides potential for outcoupling enhancement when well established outcoupling strategies (e.g., microlens arrays) are employed . It is important to note that both the thickness of the emission zone within the perovskite emitting layer and its corresponding position remain unclear in perovskite LEDs.…”

Organic Light‐Emitting Diodes: Pushing Toward the Limits and Beyond

“…Due to the immense potential for further EQE enhancement, outcoupling schemes have been studied intensively, and various structures and approaches have been reported 55,87–115. Depending on the modes targeted to extract, outcoupling structures may be classified as “internal” and “external.” That is, those extracting substrate modes are referred to as the “external” outcoupling structure and they are typically located on the opposite surface of a substrate away from the OLED stack.…”

“…Roughly speaking, internal schemes may be classified into two categories: those working within the geometrical optical domain and those working under wave‐optic principles. The former includes but is not limited to internal scattering layers, low‐index grid methods, microstructured ITO electrodes covered with conductive low‐index layers, embedded high‐index grid methods, and subelectrode microlens array 96–100. The high‐index substrate method, which removes TIR from substrate/TCO or organic layers and thus removes waveguided modes, may also be regarded as belonging to this category 101.…”

Embedding Scattering Centers in Polymer Substrate to Yield Robust Hazy Film with High Optical Transmittance: Application to Virtual‐Reality Display

“…The scattered light obscures the black matrix, so the SDE is reduced. Flexible hazy film can be achieved by surface modulation of the plastic film by using wavelength‐scale nanostructures (>700 nm) such as microlens arrays,4a–d micropyramid arrays,5 buckling structures,6 low‐index grids,7 and high‐index grids 8. Wavelength‐scale structures can scatter incident light because the period of the structure is much larger than an optical wavelength in the medium 9.…”