White organic light-emitting diodes: Status and perspective

Abstract

White organic light-emitting diodes (OLEDs) are ultra-thin, large-area light sources made from organic semiconductor materials. Over the last decades, much research has been spent on finding the suitable materials to realize highly efficient monochrome and white OLEDs. With their high efficiency, color-tunability, and color-quality, white OLEDs are emerging to become one of the next generation light sources. In this review, we discuss the physics of a variety of device concepts that are introduced to realize white OLEDs based on both polymer and small molecule organic materi als. Owing to the fact that about 80 % of the internally generated photons are trapped within the thin-film layer structure, we put a second focus on reviewing promising concepts for improved light outcoupling.Comment: 53 pages, 51 figures, to be published in Review of Modern Physic

Solution-processed multilayer small-molecule light-emitting devices with high-efficiency white-light emission

“…Despite their high mechanical robustness and compatibility with subsequent solution processing, polymers are plagued by limited reproducibility in the device performance because of batch-tobatch variations with respect to molecular weight, polydispersity, regioregularity and purity [20][21][22][23] . Moreover, their efficiencies are still far below the fluorescent tubes 24 . Thus far, the highest reported power efficiency of white polymer LEDs is B25 lm W À 1 (refs 7,25).…”

Quantum Dot/Light-Emitting Electrochemical Cell Hybrid Device and Mechanism of Its Operation

“…Light-emitting electrochemical cells (LECs) 1−4 represent a promising large-area device concept, besides organic (OLED) 5,6 and quantum dot (QD)-based light emitters (QLEDs). 6−9 The main difference to OLEDs is that the active layer comprises ionic components in addition to the lightemitting species (polymers or transition metal complexes).…”

Tuning Emission Colors from Blue to Green in Polymeric Light-Emitting Diodes Fabricated using Polyfluorene Blends

“…Different colors can be achieved by preparing different combinations of fluorescent or phosphorescent compounds, 5−21 building multilayer systems in which each layer is composed of molecules or polymers as the active medium, 4,11,13,22 combining multiple layers in a tandem diode architecture, 17 using a single polymer with multiple functional groups, 3,5,18 using mixtures of polymers with small phosphorescent 19 or fluorescent 5,20 molecules (host/guest systems), quantum dots, 22,26 or nanorods/nanotubes, 10,23 using systems with excimer or exciplex emissions, 24,25 using systems that form exciplexes in bilayer structures, 4,6 or preparing blends with conjugated polymers. 7,11,15,16,26−32 The use of polymer blends represents a relatively inexpensive approach to the preparation of novel polymeric electroluminescent (EL) diodes with acceptable performances.…”

“…7,11,15,16,26−32 The use of polymer blends represents a relatively inexpensive approach to the preparation of novel polymeric electroluminescent (EL) diodes with acceptable performances. 5,6,8 Furthermore, after the active materials are chosen, the diode architecture must be optimized to improve the device performance in terms of light output, turn-on voltage, whiteness, and brightness properties. 5,6,13,30 Polymers have emerged as a promising technology for large-area diodes and for flexible diodes, 5,33,34 which can be processed using solutionbased and conventional printing techniques (e.g., roll-to-roll or inkjet techniques).…”

“…5,6,8 Furthermore, after the active materials are chosen, the diode architecture must be optimized to improve the device performance in terms of light output, turn-on voltage, whiteness, and brightness properties. 5,6,13,30 Polymers have emerged as a promising technology for large-area diodes and for flexible diodes, 5,33,34 which can be processed using solutionbased and conventional printing techniques (e.g., roll-to-roll or inkjet techniques). 6,7,33,34 In this regard, PLEDs are an interesting target because of their ability to be easily processed using solution-based methods.…”