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

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 <i>N</i>,<i>N</i>′-di­(1-naphthyl)-<i>N</i>,<i>N</i>′-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

Data File 1: Stable angular emission spectra in white organic light-emitting diodes using graphene/PEDOT:PSS composite electrode

the CIE x- and y-coordinates at different angles (0-70°) Originally published in Optics Express on 01 May 2017 (oe-25-9-9734

Conductivity Enhancement of Nickel Oxide by Copper Cation Codoping for Hybrid Organic-Inorganic Light-Emitting Diodes

We demonstrate a Cu­(I) and Cu­(II) codoped nickel­(II) oxide (NiO_<i>x</i>) hole injection layer (HIL) for solution-processed hybrid organic-inorganic light-emitting diodes (HyLEDs). Codoped NiO_<i>x</i> films show no degradation on optical properties in the visible range (400–700 nm) but have enhanced electrical properties compared to those of conventional Cu­(II)-only doped NiO_<i>x</i> film. Codoped NiO_<i>x</i> film shows an over four times increased vertical current in comparison with that of NiO_<i>x</i> in conductive atomic force microscopy (c-AFM) configuration. Moreover, the hole injection ability of codoped NiO_<i>x</i> is also improved, which has ionization energy of 5.45 eV, 0.14 eV higher than the value of NiO_<i>x</i> film. These improvements are a consequence of surface chemical composition change in NiO_<i>x</i> due to Cu cation codoping. More off-stoichiometric NiO_<i>x</i> formed by codoping includes a large amount of Ni vacancies, which lead to better electrical properties. Density functional theory calculations also show that Cu doped NiO model structure with Ni vacancy contains diverse oxidation states of Ni based on both density of states and partial atomic charge analysis. Finally, HyLEDs of Cu codoped NiO_<i>x</i> HIL have higher performance comparing with those of pristine NiO_<i>x</i>. The current efficiency of devices with NiO_<i>x</i> and codoped NiO_<i>x</i> HIL are 11.2 and 15.4 cd/A, respectively. Therefore, codoped NiO_<i>x</i> is applicable to various optoelectronic devices due to simple sol–gel process and enhanced doping efficiency