Nanoscale Covalent Self-Assembly Approach to Enhancing Anode/Hole-Transport Layer Interfacial Stability and Charge Injection Efficiency in Organic Light-Emitting Diodes

Abstract

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.

Enhanced Polymer Light‐Emitting Diode Performance Using a Crosslinked‐Network Electron‐Blocking Interlayer

“…Inside an inert-atmosphere glove box, Ca was thermally evaporated onto the EML in a vacuum of < 10 ±6 torr using a shadow mask to define the electrode area as 10 mm 2 , and this was followed by Al-deposition to form a protective layer. Small-molecule OLED and PLED devices were characterized inside a sealed aluminum sample container in a dry-nitrogen atmosphere using a computer-controlled Keithley 2400 source meter and an IL 1700 Research Radiometer equipped with a calibrated silicon photodetector [31,32]. Dendrimers are well-defined, highly branched macromolecules with hollow cores and dense shells.…”

High‐Brightness Blue Light‐Emitting Polymer Diodes via Anode Modification Using a Self‐Assembled Monolayer

“…Inside an inert atmosphere glove box, Ca was thermally evaporated onto the PFO film in a vacuum < 10 ±6 torr, using a shadow mask to define the electrode area as 10 mm , and followed by Al deposition as a protective layer. PLED devices were characterized inside a sealed aluminum sample container using instrumentation described elsewhere [19,20]. Electroluminescence spectra were recorded within 0.5 h after device fabrication.…”

“…[17] Taking advantage of the reactive ITO surface hydroxyl groups, [19] a monolayer of silyl-functionalized TPD-like hole-transport material, TPD-Si 2 , can be hydrolytically self-assembled onto ITO via colvalent In±O±Si/Sn±O±Si linkages. The resultant smooth, contiguous, and conformal TPDSi 2 monolayer consists of a siloxane network with embedded, electroactive [20] tetraaryldiamine hole-transporting units.…”

“…[5] We also find that the SAM modification reduces local shorting currents and greatly improves device response reproducibility. This doubtless reflects the robust, conformal, and electroactive nature of the self-assembled network, [19,20] as well as the ability of such hydrophobic structures to exclude moisture. [17] That the present SAM-based device can be driven up to 7 10 ±1 A cm ±2 without obvious degradation is further evidence of its robustness.…”

Cold welding of organic light emitting diode: Interfacial and contact models

“…However, increased contact also makes it more difficult for lift-off to occur. Hence, a balance is needed between improved surface contact (for improved charge and light transport 58 ) and lift-off for interfacial separation of the stamp from the cold welded structure. This can be facilitated by the use of a layer with low adhesion energy between the stamp and the cold welded layer.…”