A new pyrene cored small organic molecule exhibiting a high PLQY and blue emission was designed and synthesized.

Two new solution processable pyrene based electroluminescent organic semiconductors (PY-PH & PY-CA) and their OLED performance reported.

In this work, three novel pyrene cored small conjugated molecules, namely 1,3,6,8-tetrakis(6-(octyloxy)naphthalene-2-yl)pyrene (PY-1), 1,3,6,8-tetrakis((E)-2-(6-(n-octyloxy)naphthalene-2-yl)vinyl)pyrene (PY-2) and 1,3,6,8-tetrakis((6-(n-octyloxy)naphthalene-2-yl)ethynyl)pyrene (PY-3) have been synthesized by Suzuki, heck and Sonogashira organometallic coupling reactions, respectively. The effects of single, double and triple bonds on their optical, electrochemical, and thermal properties are studied in detail. These are all materials fluorescent and they have been used in organic light-emitting diodes (OLEDs) and their electroluminescent properties have been studied.

Flexible multilayer thin films are promising alternatives for protecting organic light-emitting devices (OLEDs) against moisture and oxygen permeation. However, besides the inherent absorption associated with these encapsulating materials, multiple internal reflections in the multilayer configuration lead to interference effects which further modify the intensity and color balance of the transmitted light with potential detrimental effects for device performance. Accordingly, rational optimization of such system requires detail knowledge of the optical functions [n(λ), k(λ)]. Here we present a spectroscopic ellipsometry (SE) and transmission (T) study of encapsulation systems formed by up to 5 layer Units each consisting of a bilayer of sputtered co-oxide [silicon dioxide (SiO2) and aluminum oxide (Al2O3)] and fluorocarbon (CFx) prepared by plasma-enhanced chemical vapor deposition. The optical properties of each component, co-oxide and CFx, were first determined from films prepared on c-Si and glass substrates. Knowledge of the optical properties of the multilayer components was then used to simulate the transmission of completed encapsulation stacks with 1-, 2-, 3-, 4- and 5- Units. Comparison between experimental and simulated SE+T data strongly suggest that an unintended surface modification of the CFx surface results from exposure to the plasma used for co-oxide growth by magnetron sputtering. The optical functions of new phase formed (~18.2nm thick) resemble CFx but could not, however, be represented by a co-oxide — CFx effective medium approximation. Importantly, this new material was responsible for up to 20% absorption in the visible spectrum of the 5 Unit encapsulation in addition to interference effects. Incorporation of this interface layer enabled analysis (SE+T) of multi-Unit, multiangle-of-incidence analysis. Based on these results, a proposal for an encapsulation layer with average T increase from 59% to 73% over the visible spectral range is proposed by using adequate thickness of the encapsulation system to shift the interference fringes into the NIR region even in the presence of the absorbing interface layer.

Effective top-side thin film encapsulation for organic light-emitting devices (OLEDs) was achieved by deposition of a multi-layer water diffusion barrier stack to protect the device against moisture permeation. The barrier stack was formed by alternative depositions of co-oxide and fluorocarbon (CFx) films. The co-oxide layer was fabricated by magnetron co-sputtering of silicon dioxide (SiO2) and aluminum oxide (Al2O3). While the CFx layer was formed by plasma enhanced chemical vapor deposition. The water vapor transmission rate of the optimized diffusion barrier stack can be down to 10− 6 g/m2/day. The OLEDs encapsulated with the multilayer stack have been shown to have operation lifetime of over 18,000 h which is nearly the same as devices with conventional glass-cover encapsulation.

While metal diffusion in organic layers have been considered as causes for performance degradation in organic light-emitting devices, we show that suitable metal doping can instead improve physical stability of organic films. By using a metal doped organic exciton blocking layer (EBL), enhanced stability is demonstrated in unpackaged CuPc/C60 organic photovoltaic devices (OPV). While devices with a pure organic EBL of bathocuproine and tris(8-hydroxyquinolinato)aluminum (Alq3) show over ∼20% decreases in efficiency for first 150 min of operation, the device with magnesium-doped Alq3 EBL shows less than ∼5% variation in efficiency during the same period.

Deposition sequence and substrate work function in controlling the interface energy level alignment in organic photovoltaic (OPV) devices with copper phthalocyanine (CuPc) as the donor and fullerene (C-60) as the acceptor were studied using ultraviolet photoelectron spectroscopy. We found that the energy offset at the highest occupied molecular orbital of donor (HOMOD) and the lowest unoccupied orbital of acceptor (LUMOA), which limits the maximum open-circuit voltage of heterojunction OPV, can be changed from 0.64 (C-60 on CuPc) to 0.86 eV (CuPc on C-60) by reversing the deposition sequence. Furthermore, by controlling the substrate work function from 2.81 to 5.07 eV, the LUMOA-HOMOD offset can be effectively tuned from 0.86 to 1.27 eV. The results suggest that electrodes in OPV devices can have significant influences on the electronic structures and energy levels of the donor/acceptor interface, and thus provide a viable means for performance enhancement.

Silicon oxy-nitride (SiOxNy) films prepared by radio-frequency magnetron sputtering were investigated as an anode modifier in organic light-emitting diodes (OLEDs). SiOxNy films were deposited on the indium tin oxide (ITO) anode of an OLED with a configuration of ITO/SiOxNy/α-naphtylphenyliphenyl diamine (NPB)/8-hydroxyquinoline aluminum (AlQ)/Mg:Ag. By varying the argon and oxygen flow ratio during deposition of the SiOxNy films, devices with improved electroluminescent performance and operation lifetime were obtained. Atomic compositions of the SiOxNy films were analyzed with X-ray photoelectron spectroscopy. The best device with the optimized SiOxNy film showed a half brightness lifetime 5 times better than that of the control device.

Aluminum-doped zinc oxide (AZO) films were fabricated at a low substrate temperature (300 degrees C) in air by KrF excimer laser irradiation of sol-gel spin-coated films. Structural, electrical and optical properties of the laser-irradiated films at different laser energies were studied and compared with those prepared by conventional high-temperature processing. The 200 nm laser-irradiated AZO film shows a resistivity of 44 x 10(-3) Omega-cm and about 90% optical transmittance in the visible range upon laser irradiation. The films were oriented preferentially along (002) direction. (C) 2008 Elsevier B.V. All rights reserved.

Multiple fluorocarbon (CFx) and silicon nitride (Si3N4) bilayers were applied as encapsulation cap on glass-based organic light-emitting diodes (OLEDs). When CFx/Si3N4 bilayers were deposited onto the OLED structure, the devices showed performance worse than one without any encapsulation. The adverse effects were attributed to the damage caused by reaction species during the thin-film deposition processes. To solve this problem, a CuPc interlayer was found to provide effective protection to the OLED structure. With a structure of CuPc/(CFx/Si3N4)×5, the encapsulated device showed an operation lifetime over 8000 h (higher than 80% of that achieved with a conventional metal encapsulation).

A bilayer connection unit of Mg-doped Alq3 and F4-TCNQ-doped m-MTDATA was investigated for application in stacked organic light-emitting device. This connection unit led to a stacked OLED with a luminous efficiency twice that of a single-unit OLED. Electronic structures, including relevant electron energy levels, of the various interfaces in the stacked OLED were studied by using ultraviolet photoemission spectroscopy and used to discuss the working mechanisms of the stacked OLED. The p-type dopant F4-TCNQ was shown to induce a large band bending of 1.36eV and facilitates efficient carrier injection from the connection units into the carrier-transporting layers.

By using bathophenanthroline (BPhen) as an exciton blocking layer (EBL) at the organic/cathode contact of a standard copper phthalocyanine/C60 organic photovoltaic (OPV) device, power conversion efficiency was substantially increased from 0.86% to 2.64%. The BPhen-based devices showed a 45% increase in power conversion efficiency over that of an equivalent device with an EBL of bathocuproine. The performance improvement was analyzed in terms of the electron energy levels, optical transparencies and electron mobilities of the two EBLs. Based on these results, the roles of and requirements for an effective EBL were discussed. Combining the use of BPhen and a WO3 anodic buffer layer further increased the power conversion efficiency of the OPV device to 3.33%.

The effects of post-fabrication heat treatments on the performance and stability of organic light-emitting diodes (OLEDs) were studied in standard NPB/Alq3 devices. Electroluminescence (EL) performance, growth of dark spots, and operation stability of the devices with different heat-treatments were measured and monitored. It was found that optimum thermal treatment can slow down the growth of dark-spot and luminescence degradation in the OLEDs. Substantial increase in operation lifetime was also observed in the heat-treated samples. Heating at 70°C for 7.5min increases the half-brightness lifetime from 6400h (untreated device) to over 15,000h.

A black conductive electrode with a resistivity of 6.75×10−4 Ωcm was fabricated by doping silicon monoxide into aluminum by simple thermal evaporation. The relative optical reflectance of such electrode layers within the visible spectral range was between 0.12 and 0.05. The black electrode was incorporated in an organic light-emitting diode (OLED) by sequential deposition of α-napthylphenylbiphenyl diamine, tris-(8-hydroxyquinoline) aluminum and the black layer on indium-tin-oxide-coated glass substrates. The black layer reduced the reflection of ambient light entering the device and resulted in a significant increase of the OLED display contrast ratio. The electroluminescence properties of the device incorporating the black layer were investigated.

We have synthesized a small molecule fluoro-material, N,N,N′,N′-tetra(4-methylphenyl)-2,2′,3,3′,5,5′,6,6′-octafluoro-biphenyl-4,4′-diamine (POFDA), as an anode buffer layer for organic light-emitting devices (OLEDs). This fluoro-material shows obvious hydrophobicity, which stabilizes the indium-tin oxide (ITO) surface from moisture and air contaminants. In addition, insertion of an ultrathin POFDA layer at the ITO/organic interface significantly reduces operating voltage, and increase efficiency, and operational stability. Ultraviolet photoelectron spectroscopic analysis suggested that the performance improvement is related to the reduction in hole-injection barrier at the anode contact.

A flexible organic light-emitting diode (FOLED) was fabricated on a steel foil. Stainless steel foil, spin-coated polyvinyl acetate (PVA) and silicon oxide were used as a flexible substrate, an insulating planarization layer and a buffer layer, respectively. Patterned indium tin oxide (ITO) was sputter-deposited on the buffer layer to form an anode. N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and tris(8-quinolinolato) aluminum (Alq3) were used as a hole-transporting layer and a light-emitting/electron-transporting layer, respectively. A thin samarium layer was deposited on the organic stack to serve as a semitransparent cathode. The turn-on voltage of the resulting FOLED was 3V, and the light-emitting efficiency reached 0.56cd/A. The FOLED was shown to bend substantially without incurring detectable degradation.

A radio-frequency sputtering deposition method was applied to prepare indium tin oxide (ITO) on a plastic substrate, polyethylene terephthalate (PET). The correlation of deposition conditions and ITO film properties was systematically investigated and characterized. The optimal ITO films had a transmittance of over 90% in the visible range (400–700 nm) and a resistivity of 5.0×10−4 Ω-cm. Sequentially α-napthylphenylbiphenyl diamine, tris-(8-hydroxyquinoline) aluminium, and magnesium–silver were thermally deposited on the ITO-coated PET substrate to fabricate flexible organic light-emitting diodes (FOLEDs). The fabricated devices had a maximum current efficiency of ∼4.1 cd/A and a luminance of nearly 4100 cd/m2 at 100 mA/cm2. These values showed that the FOLEDs had comparable performance characteristics with the conventional organic light-emitting diodes made on ITO-coated glasses with the same device configuration.

Device stability and growth of dark spots are major concerns for the large-scale applications of organic light-emitting devices (OLEDs). OLEDs with crystalline hole-transporting layer have been fabricated by depositing organic layers at elevated substrate temperatures. Such devices showed significant improvement in electroluminescent efficiency, morphological stability, storage stability, and also retarded dark-spot growth. The lower hole mobility in crystalline NPB films is attributed to the improved device performance, leading to a better carrier balancing in the NPB/AlQ3 interface. Such crystalline NPB films also demonstrate a smoother surface, even after high-temperature annealing, and gives beneficial advantages for improving the thermal durability of OLEDs.