J. Shinar

Fabrication and electroluminescence of double-layered organic light-emitting diodes with the Al2O3/Al cathode

The effects of a controlled Al2O3 buffer layer on the behavior of highly efficient vacuum evaporated aqua regia-treated indium tin oxide (ITO)/triphenyl diamine (TPD)/8-tris-hydroxyquino-line aluminum Alq3/Al2O3/Al light-emitting diodes are described. It is found that, with a buffer layer of suitable thickness, both current injection and electroluminescence output are significantly enhanced. The enhancement is believed to be due to increased charge carrier density near the TPD/Alq3 interface that results from enhanced electron tunneling, and removal of exciton-quenching gap states that are intrinsic to the Alq3/Al interface.

Organic light-emitting devices (OLEDs) and OLED-based chemical and biological sensors: an overview

The basic photophysics, transport properties, state of the art, and challenges in OLED science and technology, and the major developments in structurally integrated OLED-based luminescent chemical and biological sensors are reviewed briefly. The dramatic advances in OLED performance have resulted in devices with projected continuous operating lifetimes of ~2 ? 105?h (~23?yr) at ~150?Cd?m?2 (the typical brightness of a computer monitor or TV). Consequently, commercial products incorporating OLEDs, e.g., cell phones, MP3 players, and, most recently, OLED TVs, are rapidly proliferating.The progress in elucidating the photophysics and transport properties, occurring in tandem with the development of OLEDs, has been no less dramatic. It has resulted in a detailed understanding of the dynamics of trapped and mobile negative and positive polarons (to which the electrons and holes, respectively, relax upon injection), and of singlet and triplet excitons. It has also yielded a detailed understanding of the spin dynamics of polarons and triplet excitons, which affects their overall dynamics significantly.Despite the aforementioned progress, there are outstanding challenges in OLED science and technology, notably in improving the efficiency of the devices and their stability at high brightness (>1000?Cd?m?2).One of the most recent emerging OLED-based technologies is that of structurally integrated photoluminescence-based chemical and biological sensors. This sensor platform, pioneered by the authors, yields uniquely simple and potentially very low-cost sensor (micro)arrays. The second part of this review describes the recent developments in implementing this platform for gas phase oxygen, dissolved oxygen (DO), anthrax lethal factor, and hydrazine sensors, and for a DO, glucose, lactate, and ethanol multianalyte sensor.

EFFECTS OF AQUAREGIA TREATMENT OF INDIUM-TIN-OXIDE SUBSTRATES ON THE BEHAVIOR OF DOUBLE LAYERED ORGANIC LIGHT-EMITTING DIODES

The effects of a controlled aquaregia treatment of indium–tin–oxide (ITO) substrates on the behavior of highly efficient vacuum evaporated double layered 8-tris-hydroxyquinoline Al (Alq3)-based light-emitting diodes are described. It is found that in suitably treated devices, both current injection and the electroluminescence (EL) are significantly enhanced. The enhancement is believed to result from the greater ITO/hole transporting layer contact areas and the contact conditions. The observed dependence of I(V), the EL output, and the EL efficiency on the ITO surface morphology indicates that space-charge-limited currents dominate the behavior of the devices.

Combinatorial fabrication and studies of bright white organic light-emitting devices based on emission from rubrene-doped 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl

Very bright and efficient white multilayer organic light-emitting devices based on orange-emitting 2–10-nm-thick layers of 0.25 and 0.5 wt % rubrene-doped 4,4′-bis(2,2′-diphenylvinyl)-1,1′biphenyl are described. The color coordinates of all but one of the devices are well within the white region at 6–12 V, corresponding to a dynamic white brightness range of 30 dB. Their highest brightness Lmax was over 74 000 Cd/m2; in all devices Lmax exceeded 50 000 Cd/m2. The maximum efficiencies were 11.0 Cd/A, 6.0 lm/W, and 4.6% at 5.8 V, 0.6 mA/cm2, and 68 Cd/m2 in the 0.25 wt %, 2-nm-thick doped layer device. The color variation is attributed to either emission from different zones in devices with a thin doped layer, or saturation of emission sites due to relatively light doping.

High-Efficiency Solution-Processed Small Molecule Electrophosphorescent Organic Light-Emitting Diodes

Extensive research on organic light-emitting diodes (OLEDs) continues due to their promise in applications such as fl at panel displays and solid state lighting. [ 1–5 ] Commonly, thermal high-vacuum evaporation technology is used for fabrication of small molecule-based OLEDs (SMOLEDs) and solution processing technology is used for those based on polymers (PLEDs). Thermal evaporation deposition enables complicated multilayer device architectures and renders excellent devices with high effi ciencies. [ 6 , 7 ] In contrast, solution-based deposition limits fabrication of composite device structures because the solvent used for one layer can redissolve or otherwise damage the previous layers. [ 8 ] Therefore, thermally evaporated SMOLEDs are typically more effi cient and longer-lived than solution-processed PLEDs. However, thermal evaporation deposition has its own disadvantages. First, it requires high vacuum and is consequently much more costly. Second, making multidopant OLEDs, such as white OLEDs (WOLEDs), requires precise control of the doping concentration of each dopant in the emitting layer (EML) to obtain the desired emission. [ 9 , 10 ] These reasons usually lead to a fabrication process of greater complexity and higher cost. On the other hand, solution processing, such as spin-coating, inkjet printing, and screen printing, is advantageous over thermal evaporation processing, due to its low-cost and large area manufacturability. [ 10 , 11 ] Additionally, it is possible to realize co-doping of several dopants by mixing the dopants and host material in solution. Hence, the fabrication of SMOLEDs via a solution process is of great importance. To that end, we demonstrate high effi ciency (forward power and luminous effi ciencies up to 60 lm W − 1 and 69 Cd A − 1 , respectively) spin-coated electrophosphorescent SMOLEDs based on greenemitting tris[2-(p-tolyl)pyridine] iridium(III) (Ir(mppy) 3 ) doped into a 4,4’-bis(9-carbazolyl)-biphenyl (CBP) host, probably due to the materials and fi lm morphology. This is the highest reported effi ciency of any solution-processed OLED and among the highest of any OLED without outcoupling enhancement. The

BRIGHT HIGH EFFICIENCY BLUE ORGANIC LIGHT-EMITTING DIODES WITH AL2O3/AL CATHODES

The behavior of bright, efficient, low-driving-voltage blue organic light-emitting diodes based on amino-oxadiazole-fluorenes (AODFs) with Al2O3/Al cathodes is described. It is shown that the thin Al2O3 buffer layer sharply enhances current injection, increases the device efficiency, and reduces the driving voltage; the performance of devices with the optimal oxide buffer layer thickness approaches those with Mg0.9Ag0.1 cathodes. The effects of the Al2O3 buffer layer are believed to result from the removal of interface gap states induced by defects and chemical bonds between the AODF and Al, which trap carriers and quench singlet excitons nonradiatively.

Combinatorial fabrication and studies of intense efficient ultraviolet–violet organic light-emitting device arrays

Arrays of ultraviolet–violet (indium tin oxide)/[copper phthalocyanine (CuPc)]/[4,4′-bis(9-carbazolyl)biphenyl (CBP)]/[2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4oxadiazole (Bu-PBD)]/CsF/Al organic light-emitting devices, fabricated combinatorially using a sliding shutter technique, are described. Comparison of the OLED electroluminescence and CBP photoluminescence spectra indicates that the emission originates from the bulk of that layer. In arrays of devices in which the thickness of the CuPc and Bu–PBD were varied, but that of CBP was fixed at 50 nm, the optimal radiance R was obtained at CuPc and Bu–PBD thicknesses of 15 and 18 nm, respectively. At 10 mA/cm2, R was 0.38 mW/cm2, i.e., the external quantum efficiency was 1.25%; R increased to ∼1.2 mW/cm2 at 100 mA/cm2.

Extremely Efficient Indium–Tin-Oxide-Free Green Phosphorescent Organic Light-Emitting Diodes

This paper demonstrates extremely efficient (η(P,max) = 118 lm W(-1) ) ITO-free green phosphorescent OLEDs (PHOLEDs) with multilayered, highly conductive poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) films as the anode. The efficiency is obtained without any outcoupling-enhancing structures and is 44% higher than the 82 lm W(-1) of similar optimized ITO-anode PHOLEDs. Detailed simulations show that this improvement is due largely to the intrinsically enhanced outcoupling that results from a weak microcavity effect.

Integrated organic light-emitting device'fluorescence-based chemical sensors

A fluorescent chemical sensor platform, integrating an organic light-emitting device (OLED) light-source with a fluorescent probe, is demonstrated for a subsecond-fast oxygen sensor. The integration results in strong light coupling and negligible heating of the sensor film or analyte. The potential in vivo operation of compact, stand-alone, battery-powered, OLED-based miniaturized sensor arrays for chemical and biological applications is discussed.

A simple biphasic route to water soluble dithiocarbamate functionalized quantum dots

Hydrophobic trioctylphosphine oxide-functionalized CdSe quantum dots (CdSe-TOPO QDs) were transferred from organic solvent to aqueous solution via a simple yet novel biphasic ligand exchange process in one step, which involved the in-situ formation of hydrophilic dithiocarbamate moieties and subsequent ligand exchange with TOPO at the chloroform/water interface. The resulting water dispersible, dithiocarbamate functionalized CdSe QDs (i.e., D-CdSe) exhibited an increased photoluminescence (PL) quantum yield as compared to the original CdSe-TOPO QDs, suggesting an effective passivation of dithiocarbamate ligands on the QD surface. The D-CdSe QDs were then mixed with hydroxyl terminated TiO2nanoparticles. A decrease in the PL of the mixture was observed, indicating a possible charge transfer from the D-CdSe QDs to the TiO2nanoparticles. The reaction of the carboxyl group on the D-CdSe surface with the hydroxyl group on the TiO2 rendered QDs in direct contact with TiO2, thereby facilitating the electronic interaction between them.