Covalently Interlinked Organic LED Transport Layers via Spin-Coating/Siloxane Condensation

Abstract

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...

Interfacial Microstructure Function in Organic Light-Emitting Diodes: Assembled Tetraaryldiamine and Copper Phthalocyanine Interlayers

“…[22] That TPD-Si 2 film coverage on ITO is conformal and largely pinhole-free is supported by studies using a previously described ferrocene probe technique. [23] The lack of significant current flow near the formal potential for ferrocene oxidation at a TPD-Si 2 -coated ITO working electrode indicates suppression of ferrocene oxidation, consistent with largely pinhole-free surface coverage. [24] The stability of device-type TPD-Si 2 /TPD interfaces under thermal stress (one measure of durability) was investigated by annealing ITO/TPD-Si 2 (40 nm)/TPD (100 nm) bilayers at 80 C for 1.0 h. The optical image of the annealed TPD film shows no evidence of TPD de-wetting/decohesion ( Fig.…”

“…Experimental Materials and Methods: The synthesis of TAA was described previously [23]. TPD, Alq, and Cu(Pc) were obtained from Aldrich and purified by gradient sublimation.…”

“…Yield, 98 %. 1 subjected to a cleaning procedure reported elsewhere [23]. TAA and TPD-Si 2 -based buffer layers were spincoated onto cleaned ITO surfaces from their respective toluene solutions (10 mg mL ±1 ) at 2 Krpm, followed by curing in moist air at 110 C for 15 min.…”

Crosslinkable hole-transporting polymers by palladium-catalyzed C—N-coupling reaction

“…13 C NMR (CDCl 3 ): d = 147.6 (C ar ); 147.2 (C ar ); 147.1 (C ar ); 146.6 (C ar ); 134.8 (C ar );134.4 (C ar ); 132.7 (C ar ); 129.3 (C ar ); 129.2 (C ar ); 128.9 (C ar ); 127.3 (C ar ); 124.4 (C ar ); 124.3 (C ar ); 124.2 (C ar ); 124.1 (C ar ); 124.0 (C ar ); 122.8 (C ar ); 78.6 (1C 6 13 C NMR (CDCl 3 ): d = 147.6 (C ar ); 147.2 (C ar ); 147.1 (C ar ); 146.7 (C ar ); 134.7 (C ar ); 133.9 (C ar ); 132.8 (C ar ); 129.2 (C ar ); 129.0 (C ar ); 128.9 (C ar ); 127.3 (C ar ); 124.4 (C ar ); 124.3 (C ar ); 124.3 (C ar ); 124.1 (C ar ); 124.1 (C ar ); 122.9 (C ar ); 78. 6 …”

“…This can be realized, for example, by conversion of a soluble precursor polymer into an insoluble form which is common for poly(p-phenylene vinylene) (PPV) 2) . Another possibility is crosslinking of suitable monomers or pre-polymers containing polymerizable moieties either as side groups or in the main chain of the polymers [3][4][5][6][7] .…”