Optical Analysis of Power Distribution in Top-Emitting Organic Light Emitting Diodes Integrated with Nanolens Array Using Finite Difference Time Domain

Abstract

Recently, we have addressed that a formation mechanism of a nanolens array (NLA) fabricated by using a maskless vacuum deposition is explained as the increase in surface tension of organic molecules induced by their crystallization. Here, as another research using finite difference time domain simulations, not electric field intensities but transmitted energies of electromagnetic waves inside and outside top-emitting blue organic light-emitting diodes (TOLEDs), without and with NLAs, are obtained, to easily grasp the effect of NLA formation on the light extraction of TOLEDs. Interestingly, the calculations show that NLA acts as an efficient light extraction structure. With NLA, larger transmitted energies in the direction from emitting layer to air are observed, indicating that NLAs send more light to air otherwise trapped in the devices by reducing the losses by waveguide and absorption. This is more significant for higher refractive index of NLA. Simulation and measurement results are consistent. A successful increase in both light extraction efficiency and color stability of blue TOLEDs, rarely reported before, is accomplished by introducing the highly process-compatible NLA technology using the one-step dry process. Blue TOLEDs integrated with a N, N'-di(1-naphthyl)- N, N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine NLA with a refractive index of 1.8 show a 1.55-times-higher light extraction efficiency, compared to those without it. In addition, viewing angle characteristics are enhanced and image blurring is reduced, indicating that the manufacturer-adaptable technology satisfies the requirements of highly efficient and color-stable top-emission displays.

Plasmonic-Enhanced Organic Light-Emitting Diodes Based on a Graphene Oxide/Au Nanoparticles Composite Hole Injection Layer

“…The improved efficiency and enhanced device stability are important for their commercialization (Coehoorn et al, 2015;Zhang et al, 2015b) Tremendous effort has been made by many researchers to enhance electroluminescent performance of OLEDs in different ways (Jesuraj et al, 2017). These efforts include heightening the internal quantum efficiency of organic materials (Adachi et al, 2001;Xiao et al, 2009), improving the out-coupling efficiency of the device with an array of lenses (Sun and Forrest, 2008;Han et al, 2018), metal nanoparticles (NPs) (Chen et al, 2017;Zhang et al, 2017), and reasonable nanostructures (Riedel et al, 2010;Chen et al, 2015).…”

12‐3: A Highly Mass‐producible Nano‐lens Array Technology for Optically Efficient Full‐color Organic Light Emitting Diode Display Applications

“…(w/o NLA: 0.012; w/ NLA: 0.006)) Table 1 summarizes current efficiencies and color coordinate change measurement (Δu′v′) values of RGB OLEDs without and with NLAs. The increase ratios of current efficiencies by NLA introduction are 1.57, 1.56 [10], and 1.59 [12], respectively, indicating similar rate of increase in the light extraction efficiencies of three color OLEDs. Thus, NLA technology can help manufacturers reduce power consumptions of full-color displays by simultaneously increasing the light extraction efficiencies of RGB OLEDs by similar percentage, to meet increasing consumer demand for low power products.…”

“…N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) powders (sublimed, purity: >99.9%) were loaded in the vaporizer to fabricate NPB NLAs. The detail procedures of OVPD were described in our previous reports [10][11][12]. The current density-voltage-luminance (J-V-L) characteristics were measured by using a Keithley 2400 programmable source meter.…”

“…1a) make manufacturers reluctant to use MLA in the industry. Very recently, we have developed a nano-lens array (NLA, lens size: <1 um) technology and obtained high-performance green [10][11] and blue OLEDs [12] by using an organic vapor phase deposition (OVPD) method. Nano-lenses having round surfaces caused OLEDs to show the significant increase in light extraction efficiencies and the improvement of color stability.…”

Very bright and efficient ITO-free narrow-spectrum micro-cavity top-emitting organic light-emitting diodes with low operation voltage

“…18 As current-driven devices, OLEDs require active-matrix display drivers to reproduce high-quality images, and the challenge is to provide a stable driving current backplane technology. 6,[19][20][21] Generally, the mobility and threshold voltage of low temperature polysilicon thin film transistors (LTPS-TFTs) are non-uniform, and uniformity compensation within the driver circuitry is required. 6,22 Most solutions aim to increase the number of TFTs in each pixel, which significantly reduces the aperture ratio of traditional bottom-emitting OLEDs (BE-OLEDs), forcing OLEDs to operate at higher brightness levels, thus shortening the lifespan.…”