Light Extraction Layer Research Articles

Finite-difference time-domain analysis on light extraction in a GaN light-emitting diode by empirically capable dielectric nano-features

Enhancement of light extraction in GaN light-emitting diode (LED) by addressing an array of nanomaterials is investigated by means of three dimensional (3D) finite-difference time-domain (FDTD) simulation experiments. The array of nanomaterials is placed on top of the GaN LED and is used as a light extraction layer. Depending on its empirically capable features, the refractive index of nanomaterials with perfectly spherical (particle) and hemispherical (plano-convex lens) shapes were decided as 1.47 [Polyethylene glycol (PEG)] and 2.13 [Zirconia (ZrO2)]. As a control experiment, a 3D FDTD simulation experiment of GaN LED with PEG film deposited on top is also carried out. Different light extraction profiles between subwavelength- and over-wavelength-scaled nanomaterials addressed GaN LEDs are observed in distributions of Poynting vector intensity of the light extraction layer–applied GaN LEDs. In addition, our results show that the dielectric effect on light extraction is more efficient in the light extraction layer with over-wavelength scaled features. In the case of a Zirconia particle array (ϕ = 500 nm) with hexagonal closed packed (hcp) structure on top of a GaN LED, light extraction along the normal axis of the LED surface is about six times larger than a GaN LED without the extraction layer.

Enhancement of light-extraction efficiency of organic light-emitting diodes using silica nanoparticles embedded in TiO₂ matrices.

We investigate two types of internal light-extraction layer structures for organic light-emitting diodes (OLEDs) that consist of silica nanoparticles (NPs) embedded in high-refractive-index TiO₂ matrices. The composite of silica NPs and TiO₂ matrices was coated on the glass substrate and fabricated with and without a SiO₂ planarization layer. An increase in the optical out-coupling efficiency by a factor of 2.0 was obtained at a high luminance of 3,000 cd/m² from OLEDs containing the silica NPs embedded in TiO₂ matrices between glass substrates and Zn-doped In₂O₃ (IZO) electrodes after additional planarization processes. This is consistent with the analytical result using the finite-difference time-domain (FDTD) method. Randomly distributed silica NPs acting as scattering centers could reduce the optical loss when extracting light. By using additional planarization processes with a PECVD-derived SiO₂ layer, one can assure that smoother surfaces provide higher out-coupling efficiency, which attain 100% and 97% enhancements in power (lm/W) and current (cd/A) efficiencies, respectively.

RCWA and FDTD modeling of light emission from internally structured OLEDs.

We report on the fabrication and simulation of a green OLED with an Internal Light Extraction (ILE) layer. The optical behavior of these devices is simulated using both Rigorous Coupled Wave Analysis (RCWA) and Finite Difference Time-Domain (FDTD) methods. Results obtained using these two different techniques show excellent agreement and predict the experimental results with good precision. By verifying the validity of both simulation methods on the internal light extraction structure we pave the way to optimization of ILE layers using either of these methods.

61.1: 80lm/W White OLEDs for Solid State Lighting

Abstract80lm/W white OLED has been successfully realized by introducing 3‐stacked tandem structure along with internal light extraction layer. The power efficacy and lifetime of the device were maintained over 80 lm/W and 26,000 hr for LT70 condition at 4,200nit operation, respectively.

Enhanced Light Out‐Coupling of OLEDs with Low Haze by Inserting Randomly Dispersed Nanopillar Arrays Formed by Lateral Phase Separation of Polymer Blends

A simple and efficient method to fabricate light extraction layers is demonstrated by utilizing the phase separation of two polymer blends to enhance the light out-coupling efficiency of OLEDs with low haze. Polystyrene and poly(methyl methacrylate) dissolved in tetrahydrofuran are mixed and spin-coated over ITO-coated glass substrates. Nanopores and nanopillar arrays are formed through lateral phase separation of the polymer blend. The shape, size, and distribution of the patterns can be controlled through changes in the composition and thickness of the coated polymer blends. Phosphorescent OLEDs are fabricated using randomly dispersed nanopillar arrays as light extraction layers and they show a 24% enhancement in external quantum efficiency with a Lambertian emission pattern, no spectrum dependence on viewing angles, and only a small increment in the haze. With these advantages, this newly developed method can be adapted to be used for large-area, flexible substrates for lighting and display applications.

60.4L: Late‐News Paper: High Efficiency 200‐lm/W Green Light Emitting Organic Devices Prepared on High‐Index of Refraction Substrate

AbstractThe total flux of the emitted light has been successfully enhanced by employing high refractive index (n=2.0) glass substrate coated with a light extraction layer. The normal CBP:Ir(ppy)3 based small molecule multilayer device exhibits a maximum external quantum efficiency of 56.9% and a power efficiency of 210‐lm/W with a threshold voltage of 2.7V. Optical mode analysis by original computer software identified the importance of the control of refractive index of substrate for total improvement of out‐coupling efficiency.