All-Solution-Processed Organic Light-Emitting Diodes Based on Photostable Photo-cross-linkable Fluorescent Small Molecules

Abstract

We demonstrate herein the fabrication of small molecule-based OLEDs where four organic layers from the hole- to the electron-transporting layers have successively been deposited by using an all-solution process. The key feature of the device relies on a novel photopolymerizable red-emitting material, made of small fluorophores substituted with two acrylate units, and displaying high-quality film-forming properties as well as high emission quantum yield as nondoped thin films. Insoluble emissive layers were obtained upon UV irradiation using low illumination doses, with no further need of postcuring. Very low photodegradation was noticed, giving rise to bright layers with a remarkable surface quality, characterized by a mean RMS roughness as low as 0.7 nm after development. Comparative experiments between solution-processed OLEDs and vacuum-processed OLEDs made of fluorophores with close architectures show external quantum efficiencies in the same range while displaying distinct behaviors in terms of current and power efficiencies. They validate the proof of concept of nondoped solution-processable emissive layers exclusively made of photopolymerized fluorophores, thereby reducing the amount of components and opening the way toward cost-effective fabrication of solution-processed OLED multilayer architectures.

Recent Advances in Polymer Organic Light-Emitting Diodes (PLED) Using Non-conjugated Polymers as the Emitting Layer and Contrasting Them with Conjugated Counterparts

“…23) which generated an excellent film after ultraviolet irradiation with a R q (rootmean-square surface roughness) as low as 0.7 nm. 92 The film showed a k PL at 635 nm with a high U PL of 37%. An all-solution-processed device [ITO/PED-OT:PSS (40 nm)/QUPD (35 nm)/FVIN-A (25 nm)/ TPBI (50 nm)/LiF (1 nm)/Al (100 nm)] showed k EL and CIE at 600 nm and (0.54, 0.45), respectively, where QUPD is a commercial cross-linkable holetransporting material first reported by Yang and coworkers.…”

“…89,90 However, the main obstacle is the dissolution of the previous organic layer by the solvent used for the deposition of the current layer. One resolution is to first spincast cross-linkable materials on the substrate followed by thermal- 91 or photo-induced 92,93 crosslinking so as to transform them into an insoluble polymeric layer. The main advantage of the crosslinking approach over other methods such as use of orthogonal solvent 94 and polyelectrolyte route 95 is that the intractable cross-linked layer is resistant to all organic solvents.…”

“…On the other hand, in some cases thermal-or photo-induced cross-linking can cause damage to the organic materials of the device. 92 Derue et al prepared a cross-linkable orange-red emitter FVIN-A (Fig. 23) which generated an excellent film after ultraviolet irradiation with a R q (rootmean-square surface roughness) as low as 0.7 nm.…”

Toward high volume solution based roll-to-roll processing of OLEDs

“…6 Although these processes are well-established, device fabrication by solution processing, i.e., by printing and coating of functional inks, has emerged as a promising alternative route toward industrial mass production of organic optoelectronic devices. [7][8][9][10] For solution processing on the academic laboratory scale, spin coating is frequently the method of choice for the thin layer deposition due to its ease of application and its good control over the layer thickness and homogeneity. 10 For industrial production, however, it suffers from its lack of compatibility with high volume manufacturing and its inefficient use of materials.…”

“…[7][8][9][10] For solution processing on the academic laboratory scale, spin coating is frequently the method of choice for the thin layer deposition due to its ease of application and its good control over the layer thickness and homogeneity. 10 For industrial production, however, it suffers from its lack of compatibility with high volume manufacturing and its inefficient use of materials. Research aimed at results more directly applicable in an industrially relevant production environment therefore focuses on other techniques, like slotdie coating.…”