The integrity of anode/organic interfacial contact is shown to be crucial to the performance and stability of archetypical small molecule organic light-emitting diodes (OLEDs). In this contribution, vapor-deposited lipophilic, hole-transporting 1,4-bis(phenyl-m-tolylamino)biphenyl (TPD) and 1,4-bis(1-naphthylphenylamino)biphenyl (NPB) thin films are shown to undergo decohesion on ITO anode surfaces under mild heating. An effective approach to ameliorate such interfacial decohesion is introduction, via self-assembly or spin-coating, of covalently bound N(p-C6H4CH2CH2CH2SiCl3)3 (TAA)- and 4,4‘-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si2)-derived adhesion/injection layers at the anode/hole transport layer interface. The resulting angstrom-scale hole transport layers prevent decohesion of vapor-deposited hole transport layers and significantly enhance OLED hole injection fluence. OLEDs fabricated with these modified interfaces exhibit appreciably reduced turn-on voltages, considerably higher luminous intensities, and enhanced thermal robustness versus bare ITO-based control devices. Spin-coated, cross-linked TPD-Si2 films, in particular, prove to be superior to conventional ITO functionalization interlayers, including copper phthalocyanine, in this regard. The present ITO-functionalized devices achieve maximum external forward quantum efficiencies as high as 1.2% and a luminous level of 15 000 cd/m2 in simple ITO/interlayer/HTL/Alq/Al heterostructures. We also show that Cu(Pc) interlayers actually suppress, rather than enhance, hole injection and template crystallization of vapor-deposited TPD and NPB at modest temperatures, resulting in poor OLED thermal stability.

The integrity of electrode/organic interfacial contact is shown to be crucial to the performance and stability of organic light-emitting diodes (OLEDs). In this contribution, vapor-deposited lipophilic, holetransporting N,N′-diphenyl-N, N′-bis(3-methylphenyl)[1,1′-biphenyl]-4,4′-diamine (TPD) films are shown to undergo dewetting on indium tin oxide (ITO) anode surfaces under mild heating. An effective approach to minimize this interfacial decohesion effect is by small hole transport molecule self-assembly on the anode surface. Thus, conformal N(p-C6H4CH2CH2CH2SiCl3)3 (TAA)-based monolayers can be covalently self-assembled from solution onto hydroxylated ITO surfaces. The resulting nanometer-scale-thick TAA layers (∼11 Å/layer) prevent dewetting of the vapor-deposited TPD hole transport layers. Furthermore, ITO/(TAA)n/TPD/Alq/Al structured OLED devices fabricated with these modified ITO-TPD interfaces exhibit, as a function of n, reduced turn-on voltages as well as considerably higher luminous intensities and thermal stabilities compared to bare ITO-based devices.

Modification of the anode (usually Sn-doped In 2 O 3 , ITO)-organic interface in organic light-emitting diode (OLED) structures by chemisorption/self-assembly of nanoscopic adsorbate layers can effect dramatic enhancements in device performance for reasons that are variously associated with balancing holeelectron injection fluences, 1 altering the anode work function, 2 electric field effects, 3 anode chemical passivation, 1a improving anode wetting by the hole transport layer, 4 and smoothing interlayer HOMO energetic discontinuities. 5 In principle, the nanoscale charge-blocking modulation possible via such interfacial effects combined with soft lithographic techniques such as microcontact printing (µCP) 6 should offer an easily implemented alternative/complement to/improvement over current approaches 7-13 for patterning OLEDs. The attraction versus several current approaches includes smaller feature sizes, parallel rather than serial fabrication, nanoscale interface tailorability, and potential molecular recognition characteristics. However, achieving rapid, contiguous anode coverage requires addressing poorly understood features of ITO surface chemistry which appear to limit efficient chemisorption. 2,14 We report here an approach to OLED anode patterning using high-temperature microcontact printing (or hot microcontact printing, HµCP) which readily affords pixel features down to 1.0 µm dimensions 15 and which, by virtue of the length scale-dependent carrier tunneling through SAM structures, 16 affords tunability in luminescent patterns.The mold for the PDMS µCP "stamp" was fabricated using standard photolithographic techniques and a vapor-deposited, CF 3 (CF 2 ) 5 CH 2 CH 2 SiCl 3 -derived release SAM. 6b,17 The test pattern consisted of arrays of cylinders with diameters ranging from 1 to 40 µm and with 100 µm center-to-center distances. A series of freshly distilled RSiCl 3 reagents (R ) n-CH 3 (CH 2 ) n -(n ) 21, 17, 7), n-CF 3 (CF 2 ) 5 CH 2 CH 2 -) as solutions in dry hexane were used as "inks", and were applied under rigorously anaerobic conditions to the PDMS stamp, followed by spinning at 2000 rpm for 60 s. After application of the test patterned SAMs to cleaned, 3-4 nm rms roughness, 2.5 cm 2 ITO-glass substrates (vide infra), standard OLED structures were fabricated in a double evaporator-interfaced glovebox as described elsewhere 1a,18 using vapor deposited layers of gradient sublimed TPD (50 nm) and Alq 3 (60 nm) as hole transport and electron transport/emission layers, respectively. Vapor deposition of a 70-100 nm Al cathode completed the device. Device characterization was carried out in the continuous dc mode using a Tektronix PS281 power supply and a calibrated Si photodiode. I-V responses were recorded using a Keithley 2400 current source.Initially, all attempts to transfer an RSiCl 3 -derived pattern to ITO substrates using standard µCP methodologies (stamping performed in ambient or in a glovebox; ink in various solvents at various concentrations; stamping for short or long times using an ...

The background pressure in the deposition system prior to device fabrication was normally 6´10 ±6 Torr, and the pressure during film deposition was between 6´10 ±6 and 1´10 ±5 Torr. The compounds used for fabrication of the devices were evaporated from resistively heated tantalum boats onto the substrates at room temperature. 4,4¢-Di(phenyl-a-napthylamino)biphenyl (a-NPD) and aluminum-tris(8-quinoloxide) (Alq 3 ) were deposited successively at a rate of 0.8±2 /s to give films of thickness 400 and 500 respectively. After deposition of the organic films, the chamber was vented and a shadow mask was put onto the substrates to pattern the cathodes as 1 mm diameter dots. Magnesium and silver were then co-deposited at a rate of 2 /s for magnesium and 0.15±0.2 /s for silver. The corresponding ratio of Mg:Ag was close to 10:1. The thickness of this layer was 800±1000 .In each experiment two devices were made at the same time. One was a ITO/a±NPD/Alq 3 /Mg±Ag device used as a reference. The other one was TiN/a±NPD/Alq 3 /Mg±Ag.The devices were characterized in air within 4 h of fabrication. Current± voltage measurements were made with a Keithley source meter (model 2400). Light intensity was measured using a Newport model 1835 optical power meter and silicon radiometer. EL spectra were measured with a Photon Technology International fluorimeter. Optical transmittance at 632 nm was also measured using a He-Ne laser and photodetector.Organic light emitting diodes (OLEDs) continue to make impressive advances in both vacuum-deposited small molecule [1±5] and spin-coated polymeric [5±8] configurations. Nevertheless, optimum devices will require addressing a number of critical materials challenges, including minimization of pinholes, shorting, interlayer diffusion, electrode± layer and/or layer±layer delamination, thermal, chemical, and environmental degradation, not to mention development of efficient fabrication processes. In this communication, we report an approach to OLED hole transport layer (HTL) deposition in which triarylamine core structures are functionalized with highly reactive silane groups which undergo rapid crosslinking and densification as the HTL layer is spincoated. The result after thermal curing is a robust, adherent, essentially pinhole-free charge transporting network embedded in a matrix of the type employed for high-temperature/high-dielectric strength insulators and spin-on glasses. [9] We also communicate here the properties of the first OLEDs fabricated with such a crosslinked HTL component.Trichlorosilane-functionalized triarylamine II was synthesized (Scheme 1; see Experimental for details) by allylation [10,11] of tris(4-bromophenyl)amine to yield tris(4-allylphenyl)amine (I), which after chromatographic purification, was subjected to catalytic hydrosilylation. [12,13] HTL precursor II is a pale-yellow, air-sensitive oil which was purified by vacuum distillation, and was characterized by 1 H NMR, mass spectrometry, and elemental analysis. In the presence of moisture, e.g., during spin-coati...

The proton's tensor charges are calculated at leading order in a symmetry-preserving truncation of all matter-sector equations relevant to the associated bound-state and scattering problems. In particular, the nucleon three-body bound-state equation is solved without using a diquark approximation of the two-body scattering kernel. The computed charges are similar to those obtained in contemporary simulations of lattice-regularised quantum chromodynamics, an outcome which increases the tension between theory and phenomenology. Curiously, the theoretical calculations produce a value of the scale-invariant ratio (−δT d/δT u) which matches that obtained in simple quark models, even though the individual charges are themselves different. The proton's tensor charges can be used to constrain extensions of the Standard Model using empirical limits on nucleon electric dipole moments.