The photo and electroluminescent properties of a single-layer multi-component blend composed of only blue and red emitters were studied. The blue emitter poly(9,9-dihexyl-2,7-fluorene)] (LaPPS10) was used as the matrix, and the two red emitters, poly[2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH-PPV) and 4-(dicyanomethylene)-2-methyl-6-(dimethylaminostyryl)-4H-pyrane (DCM), as the dopants. A detailed study of this system was performed in solution and in the solid state, comparing the photophysics aspects of emission spectra of the blend and those of the matrix with each one of the components. The white OLED device exhibited CIE chromaticity coordinates x = 0.30 and y = 0.31. Electro and photoluminescence emission profiles were discussed.; CNPq; FAPESP; Instituto Nacional de Ciência e Tecnologia em Eletrônica Orgânica (INEO)
Poly(p-phenylene vinylene) (PPV) derivatives are well known for their applications in polymer light emitting diodes (PLEDs). These derivatives are highly susceptible to photooxidation though, which is mainly caused by the scission of the vinyl double bond on the polymer backbone. In this work, we show that Langmuir-Blodgett (LB) films are less degraded than cast films of a PPV derivative (OC1OC6-PPV). Both films had similar thickness (∼50 nm) to allow for a more realistic comparison. Photodegradation experiments were carried out by illuminating the films with white light from a halogen lamp (50W, 12 V), placed at a fixed dstance from the sample. The decay was monitored by UV-Vis and FTIR spectroscopies. The results showed that cast films are completely degraded in ca. 300 min, while LB took longer times, ca. 1000 min, i.e. 3 times the values for the cast films. The degradation process occurs in at least two stages, the rates of which were calculated assuming that the reaction follows a first order kinetics. The characteristic times for the first stage were 3.6×10-2 and 1.3×10-3 min-1 for cast and LB films, respectively. For the second stage the characteristic times were 5.6×10-2 and 5.0×10 -3 min-1. The differences can be attributed to the more compact morphology in the LB than in the cast films. With a compact morphology the diffusion of oxygen in the LB film is hampered and this causes a delay in the degradation process.
The development of efficient organic light-emitting diodes (OLED) and organic photovoltaic cells requires control over the dynamics of spin sensitive excitations. Embedding heavy metal atoms in π-conjugated polymer chains enhances the spin-orbit coupling (SOC), and thus facilitates intersystem crossing (ISC) from the singlet to triplet manifolds. Here we use various nonlinear optical spectroscopies such as two-photon absorption and electroabsorption in conjunction with electronic structure calculations, for studying the energies, emission bands and ultrafast dynamics of spin photoexcitations in two newly synthesized π-conjugated polymers that contain intrachain platinum (Pt) atoms separated by one (Pt-1) or three (Pt-3) organic spacer units. The controllable SOC in these polymers leads to a record ISC time of <~1 ps in Pt-1 and ~6 ps in Pt-3. The tunable ultrafast ISC rate modulates the intensity ratio of the phosphorescence and fluorescence emission bands, with potential applications for white OLEDs.
Highly efficient organic light emitting diodes (OLEDs) based on multiple layers of vapor evaporated small molecules, indium tin oxide transparent electrode, and glass substrate have been extensively investigated and are being commercialized. The light extraction from the exciton radiative decay is limited to less than 30% due to plasmonic quenching on the metallic cathode and the waveguide in the multi-layer sandwich structure. Here we report a flexible nanocomposite electrode comprising single-walled carbon nanotubes and silver nanowires stacked and embedded in the surface of a polymer substrate. Nanoparticles of barium strontium titanate are dispersed within the substrate to enhance light extraction efficiency. Green polymer OLED (PLEDs) fabricated on the nanocomposite electrode exhibit a maximum current efficiency of 118 cd/A at 10,000 cd/m2 with the calculated external quantum efficiency being 38.9%. The efficiencies of white PLEDs are 46.7 cd/A and 30.5%, respectively. The devices can be bent to 3 mm radius repeatedly without significant loss of electroluminescent performance. The nanocomposite electrode could pave the way to high-efficiency flexible OLEDs with simplified device structure and low fabrication cost.
Purpose. To determine whether organic electroluminescence (OLED) screens can be used as visual stimulators to elicit pattern-reversal visual evoked potentials (p-VEPs). Method. Checkerboard patterns were generated on a conventional cathode-ray tube (S710, Compaq Computer Co., USA) screen and on an OLED (17 inches, 320 × 230 mm, PVM-1741, Sony, Tokyo, Japan) screen. The time course of the luminance changes of each monitor was measured with a photodiode. The p-VEPs elicited by these two screens were recorded from 15 eyes of 9 healthy volunteers (22.0 ± 0.8 years). Results. The OLED screen had a constant time delay from the onset of the trigger signal to the start of the luminescence change. The delay during the reversal phase from black to white for the pattern was 1.0 msec on the cathode-ray tube (CRT) screen and 0.5 msec on the OLED screen. No significant differences in the amplitudes of P100 and the implicit times of N75 and P100 were observed in the p-VEPs elicited by the CRT and the OLED screens. Conclusion. The OLED screen can be used as a visual stimulator to elicit p-VEPs; however the time delay and the specific properties in the luminance change must be taken into account.
Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.
The objective of this thesis was to explore the chemistry of series of linear and star shaped compounds based on benzimidazolyl, 2-(2’-pyridyl)benzimidazolyl, and 2,2’-dipyridylamino functional groups. These groups all possess Lewis base sites suitable for metal coordination, and are all known fluorophores.
The first compounds to be presented are the homo-substituted benzimidazolyl derivatives. Compounds 2.1-2.5 have been fully characterized and are all luminescent with emission energies in the UV region. While coordination complexes with these ligands have not been isolated, the effect of metal ion complexation on ligand luminescence has been explored via metal ion titration experiments. Furthermore, these compounds all have electron affinities greater than -3.0 eV and large optical bandgaps that range between 3.55 and 3.95 eV. These compounds also have high thermal and morphological stability. In light of this, compound 2.3 was selected as a representative example, and further characterized as an electron transport/hole blocking material for OLED applications. It has demonstrated a performance comparable to that of the well known electron transport material Alq3 (q = 8-hydroxyquinolinate).
The second class of compounds...
Neste trabalho foi desenvolvido um emissor W-OLED (white organic light
emitting diode) para aplicações em iluminação genérica, recorrendo a dois
materiais orgânicos emissores em cores complementares, NPB (N,N′-Bis
(naphthalen-1-yl)-N, N′-bis(phenyl)benzidine) e DCM1 (4-(Dicyanomethylene)-
2-methyl-6-(4-dimethylaminostyryl)-4H-pyran), o primeiro emissor na região do
azul-verde e o segundo na região vermelha do espectro eletromagnético. Foi
feito um estudo do desempenho para diferentes espessuras da camada ativa
em dois tipos de substratos: rígido (vidro) e flexível (PET). Os dispositivos
foram caracterizados no seu comportamento corrente – tensão, espectro de
eletroluminescência, coordenadas de cor, luminância e eficiência luminosa. Foi
feito um estudo complementar do TCO usado como contacto, tanto no vidro
como no PET. O melhor resultado foi obtido para 400Å espessura da camada
ativa, tanto em substrato de vidro como PET. Em substrato de vidro obteve-se
uma luminância máxima de 351,5 Cd/m2 e coordenadas de cor x=0.335
y=0.408.; We have developed a W - OLED (organic light emitting diode white) for general
lighting applications, using two organic materials emitting in complementary
colors, NPB (N,N' - Bis(naphthalen-1-yl)-N...
Efficient phosphorescent orange, blue and white organic light-emitting devices (OLEDs) with non-doped emissive layers were successfully fabricated. Conventional blue phosphorescent emitters bis [4,6-di-fluorophenyl]-pyridinato-N,C2′] picolinate (Firpic) and Bis(2,4-difluorophenylpyridinato) (Fir6) were adopted to fabricate non-doped blue OLEDs, which exhibited maximum current efficiency of 7.6 and 4.6 cd/A for Firpic and Fir6 based devices, respectively. Non-doped orange OLED was fabricated utilizing the newly reported phosphorescent material iridium (III) (pbi)2Ir(biq), of which manifested maximum current and power efficiency of 8.2 cd/A and 7.8 lm/W. The non-doped white OLEDs were achieved by simply combining Firpic or Fir6 with a 2-nm (pbi)2Ir(biq). The maximum current and power efficiency of the Firpic and (pbi)2Ir(biq) based white OLED were 14.8 cd/A and 17.9 lm/W.
Exploiting our recently developed bilayer interface methodology, together with a new wide energy-gap, low LUMO acceptor (A) and the designated donor (D) layers, we succeeded in fabricating an exciplex-based organic light-emitting diode (OLED) systematically tuned from blue to red. Further optimization rendered a record-high blue exciplex OLED with ηext of 8%. We then constructed a device structure configured by two parallel blend layers of mCP/PO-T2T and DTAF/PO-T2T, generating blue and yellow exciplex emission, respectively. The resulting device demonstrates for the first time a tandem, all-exciplex-based white-light OLED (WOLED) with excellent efficiencies ηext: 11.6%, ηc: 27.7 cd A−1, and ηp: 15.8 ml W−1 with CIE(0.29, 0.35) and CRI 70.6 that are nearly independent of EL intensity. The tandem architecture and blend-layer D/A (1:1) configuration are two key elements that fully utilize the exciplex delay fluorescence, providing a paragon for the use of low-cost, abundant organic compounds en route to commercial WOLEDs.
We described an approach to achieve fine color control of fluorescent White
Organic Light-Emitting Diodes (OLED), based on an Ultra-thin Premixed emitting
Layer (UPL). The UPL consists of a mixture of two dyes (red-emitting
4-di(4'-tert-butylbiphenyl-4-yl)amino-4'-dicyanovinylbenzene or fvin and
green-emitting 4-di(4'-tert-butylbiphenyl-4-yl)aminobenzaldehyde or fcho)
premixed in a single evaporation cell: since these two molecules have
comparable structures and similar melting temperatures, a blend can be
evaporated, giving rise to thin films of identical and reproducible composition
compared to those of the pre-mixture. The principle of fine color tuning is
demonstrated by evaporating a 1-nm-thick layer of this blend within the
hole-transport layer (4,4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl
(\alpha-NPB)) of a standard fluorescent OLED structure. Upon playing on the
position of the UPL inside the hole-transport layer, as well as on the premix
composition, two independent parameters are available to finely control the
emitted color. Combined with blue emission from the heterojunction, white light
with Commission Internationale de l'Eclairage 1931 color coordinates (0.34,
0.34) was obtained, with excellent color stability with the injected current.
The spectrum reveals that the fcho material does not emit light due to
efficient energy transfer to the red-emitting fvin compound but plays the role
of a host matrix for fvin...
This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/aic.14777.; The dataset associated with this article can be found on the Cambridge University Repository at https://www.repository.cam.ac.uk/handle/1810/249116.; Controlling the final shape resulting from evaporation of pinned droplets containing polymer, is important in the fabrication of P-OLED displays by inkjet printing. Typically, a coffee - ring shape arises, due to the pinning and associated outward capillary flow. For operational reasons, this is undesirable ? a flat topography is required. The aim of this work is to understand the important groups governing the shape, to provide a practical guide to ink selection. The theory presented is based on a thin-film lubrication model. The governing equations are solved numerically and continuously track the lateral progression of a liquid/gel front. A large capillary number or large ratio of initial to maximal polymer volume fraction can suppress the coffee-ring. White light interferometry is used to confirm these findings experimentally.; This research has been funded by the Engineering & Physical Sciences Research Council, UK and CASE studentship funding from Cambridge Display Technology Ltd....
White Color tuning is an attractive feature that Organic Light Emitting Diodes (OLEDs) offer. Up until now, there hasn’t been any report that mix both color tuning abilities with device stability. In this work, White OLEDs (W-OLEDs) based on a single RGB blend composed of a blue emitting N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) doped with a green emitting Coumarin-153 and a red emitting 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM1) dyes were produced. The final device structure was ITO/Blend/Bathocuproine (BCP)/ Tris(8-hydroxyquinolinato)aluminium (Alq3)/Al with an emission area of 0.25 cm2. The effects of the changing in DCM1’s concentration (from 0.5% to 1% wt.) allowed a tuning in the final white color resulting in devices capable of emitting a wide range of tunes – from cool to warm – while also keeping a low device complexity and a high stabilitty. Moreover, an explanation on the optoelectrical behavior of the device is presented. The best electroluminescense (EL) points toward 160 cd/m2 of brightness and 1.1 cd/A of efficiency, both prompted to being enhanced. An Impedance Spectroscopy (IS) analysis allowed to study both the effects of BCP as a Hole Blocking Layer and as an aging probe of the device. Finally...