We report multilayer nanocrystal quantum dot light-emitting diodes (QD-LEDs) fabricated by spin-coating a monolayer of colloidal CdSe/CdS nanocrystals on top of thermally polymerized solvent-resistant hole-transport layers (HTLs). We obtain high-quality QD layers of controlled thickness (down to submonolayer) simply by spin-coating QD solutions directly onto the HTL. The resulting QD-LEDs exhibit narrow ( approximately 30 nm, fwhm) electroluminescence from the QDs with virtually no emission from the organic matrix at any voltage. Using multiple spin-on HTLs improves the external quantum efficiency of the QD-LEDs to approximately 0.8% at a brightness of 100 cd/m(2) (with a maximum brightness over 1,000 cd/m(2)). We conclude that QD-LEDs could be made more efficient by further optimization of the organic semiconductors.

No abstract

High‐efficiency white polymer light‐emitting diodes are demonstrated by using a hole‐injection/transport bilayer. The excellent solvent resistance of the fully crosslinked hole‐injection layer ensures the subsequent solution processing of the light‐emitting layer. High power efficiency can be achieved. The device also emits quite stable white light. The figure shows a schematic of the device and the chemical structure of the VB‐TCTA layer.

During the past decade, significant improvements in polymer light-emitting diodes (PLEDs), including good efficiency, high brightness, and low drive voltage, have led to the realization of high-efficiency, full-color, and white-color PLEDs. [1,2] In spite of all these advancements, operational stability is still quite challenging for PLED technology. To achieve high efficiency, low-work-function metals (such as Ca or Ba) are widely used as a cathode to facilitate electron injection. [3] These metals are very sensitive to moisture and oxygen and form detrimental quenching sites at areas near the interface between the electroluminescence (EL) layer and the cathode. In addition, metal ions formed at the metal/organic interface tend to migrate into the EL layer, thus, affecting the longterm stability of devices. [4] To circumvent these problems, it is desirable to use highwork-function metals (such as Al, Ag, or Au) as the cathode because of their better environmental stability and the simplicity of their device fabrication. To improve electron injection from high-work-function metals into the emitting layer, numerous approaches have been attempted. [5][6][7][8] For example, by inserting a thin layer of polar or ionic insulating species, such as lithium fluoride (LiF), [6] cesium fluoride (CsF), [7] or organic surfactants, [8] between Al and the light-emitting layer, the electron-injection ability could be significantly improved. However, all these methods exhibit cathode dependence and they could not be applied to other high-work-function metals such as Ag or Au. Until recently, ammonium-functionalized cationic polyfluorenes surfactants and their precursors have been found to exhibit excellent electron-injection (or transport) ability in PLEDs. [9][10][11][12] They could be utilized in devices with Al or high-work-function Ag or Au as the cathode.[13]Nevertheless, they encounter the same problems of counterions of these organic surfactants migrating into the EL layer and affecting the long-term stability of the devices. [14] In addition, the electron-injection ability of these polymer electrolytes is also strongly influenced by the nature of their counterions. [15] As an alternative, neutral insulting surfactants were employed for high-work-function metal cathodes in PLEDs. [16,17] Since most of these neutral surfactants are based on poly(ethylene glycol) (PEG)-or poly(propylene glycol) (PPG)-like materials, they only form a good coordination with Al metal. Moreover, because of their insulating nature, the performance of the LEDs is affected significantly when their thickness is not properly controlled. [18] In this Communication, we report the synthesis and characterization of a neutral, conjugated surfactant, poly[9,9-bis(6′-(diethanolamino)hexyl)fluorene] (PFN-OH), comprising a conjugated fluorene main chain and a surfactant-like side chain, which was made by the palladium-catalyzed Suzuki coupling reaction. Compared to the previously reported neutral surfactants, there are several advantages of using PFN-OH as a...

A convenient approach to novel Eu3+-grafting conjugated polymers to achieve sharp red emission for polymeric light emitting diodes (PLEDs) has been developed in this contribution. The structure of polymer 1 is verified by FT-IR, 1H, 13C NMR and elemental analysis. The results indicate that efficient intramolecular Föster energy transfer depends on the overlap between the fluorescent spectrum of polymer 1 and absorption spectrum of Eu3+ chelates. Eu(DBM)3 is obviously the best one for accepting energy from polymer 1 among three Eu3+ chelates to exhibit the sharp red emission. The investigation also shows that the efficiency of energy transfer relies on the content of Eu3+ in the complexes. The investigations on the photophysical and electrochemical properties also show that the HOMO and LUMO energy levels and the band gap of complexes have no alteration with the attachment of the Eu3+ chelate in comparison with those of polymer 1 due to the Eu3+ chelate at the side chain of the whole molecule. The pure red electroluminescence is achieved from the fabrication of PLEDs using complex 5 as the active layer with the configuration of ITO/PVK/complex 5/Ba/Al.