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

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.