Enhanced light emission from top-emitting organic light-emitting diodes by optimizing surface plasmon polariton losses

Abstract

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.

High‐Efficiency Sky Blue to Ultradeep Blue Thermally Activated Delayed Fluorescent Diodes Based on Ortho‐Carbazole‐Appended Triarylboron Emitters: Above 32% External Quantum Efficiency in Blue Devices

“…Optical Simulation : For optical analysis, a power dissipation spectra simulation was performed on the basis of an advanced classical dipole model that considers the Purcell effect, surface plasmon polariton (SPP) light loss, waveguide modes, the dipole orientation effect, and so on . In optical simulation, the refractive indices of the used materials were obtained by spectroscopic ellipsometry, and the emission zone was positioned at an optimized distance in the emission layer to maximize the two‐beam constructive interference.…”

Efficiency of Light Outcoupling Structures in Organic Light‐Emitting Diodes: 2D TiO2 Array as a Model System

“…Compared to silver, the first-order cavity gets slightly more efficient with aluminum. [47] Second, the reflectivity of aluminum is not as high as that of silver in the visible range of the electromagnetic spectrum. At the same time, the values for the second-order drop to 34% (vs 35%) and 50% (vs 52%), respectively.…”

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

“…In fact, replacing one of the transport layers with a low‐index layer is receiving some attention as an effective method by which SPP mode can be reduced while maintaining a planar structure 58,59. In particular, the effect can become most significant when organic layers adjacent to metallic electrodes, i.e., electron transport or injection layer (ETL or EIL) for a p–i–n structure; and hole transport layer (HTL) or HIL for an n–i–p structure, have relatively low refractive index 66. In a simple configuration where a half‐space filled with a dielectric medium having a relative permittivity of ε d and the other half space filled with a metal with a relative permittivity of ε m , the dispersion relation of SPP wavevector k SPP along the interface is given by where ω and c are the angular frequency and the speed of light, respectively 27,55,59,66,67.…”