Blue Single-Layer Organic Light-Emitting Diodes Using Fluorescent Materials: A Molecular Design View Point

Since the beginning of organic light-emitting diodes (OLEDs), blue emission has attracted the most attention and many research groups worldwide have worked on the design of materials for stable and highly efficient blue OLEDs. However, almost all the high-efficiency blue OLEDs using fluorescent materials are multilayer devices, which are constituted of a stack of organic layers to improve the injection, transport, and recombination of charges within the emissive layer. Although the technology has been mastered, it suffers from real complexity and high cost and is time-consuming. Simplifying the multilayer structure with a single-layer one, the simplest devices made only of electrodes and the emissive layer have appeared as an appealing strategy for this technology. However, removing the functional organic layers of an OLED stack leads to a dramatic decrease of the performance and achieving high-efficiency blue single-layer OLEDs requires intense research especially in terms of materials design. Herein, an exhaustive review of blue emitting fluorophores that have been incorporated in single-layer OLEDs is reported, and the links between their electronic properties and the device performance are discussed. Thus, a structure/properties/device performance relationship map is drawn, which is of interest for the future design of organic materials.