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Charge-transporting organic semiconductors are an important class of materials that play crucial roles in electronic and optoelectronic devices such as organic light-emitting devices (OLEDs), [1] thin film transistors, and photovoltaic cells.OLEDs, that have organic hole-and electron-transport layers sandwiched between two electrodes, show low driving voltage and bright emission and are of importance for application to full color flat-panel displays and lighting. Since electron mobilities in organic materials, in general, are several orders of magnitude lower than hole mobilities, [2] electron-transport materials (ETMs) with high electron mobility are required to further improve OLED performance. To achieve an effective electron injection and transport in an OLED, a high conductive n-doped electron-transport layer is developed by Kido [3] and Leo [4,5] by coevaporation of ETM and highly active alkaline metal of Li and Cs. In this case, a hole-and exciton-block buffer layer is indispensable to prevent exciton quenching in the emissive layer by the dopants in the electron-transport layer. This may induce more complexity of device structure and thus higher cost for applications to flat-panel displays and lighting. Forrest and Thompson's group has proposed a way to break through the efficiency limitation by using phosphorescent emitting materials. This renders possible harvesting both electro-generated singlet and triplet excitons for emission from OLEDs and realizing nearly 100% internal quantum efficiencies of electroluminescence. [6,7] It is essential that the triplet excited states of all the corresponding materials should be higher than that of the phosphorescent emitter to confine the generated triplet excitons in the emissive layer. To match this request, the conjugation length of the material must be limited to achieve high triplet energy levels. However, it is difficult to meet these requirements because there is a tradeoff between increasing the band gap of the material to increase singlet and triplet energies and decreasing the p-conjugation system, which may adversely affect the charge transport properties.[8]As such, it becomes particularly challenging to develop carrier transport materials with high triplet energy levels especially for a blue triplet emitter. In this communication, we report two pyridine-containing triphenylbenzene derivatives of 1,3,5-tri(m-pyrid-3-yl-phenyl) benzene (TmPyPB) and 1,3,5-tri( p-pyrid-3-yl-phenyl)benzene (TpPyPB), which possess both high electron mobilities and high triplet energy levels. High external quantum efficiency and power efficiency are realized for the iridium (III) bis(4,6-(di-fluorophenyl)pyridinato-N,C 2 0 ) picolinate (FIrpic)-based blue phosphorescent OLED and the fac-tris(2-phenylpyridine) iridium (Ir(PPy) 3 )-based green phosphorescent OLED using TmPyPB and TpPyPB as the ETMs, respectively.Scheme 1 depicts the synthetic routes of TmPyPB and TpPyPB. They were synthesized by the Suzuki cross-coupling reaction between 3-(4,4,5,5-tetramethyl-1,3,2-dioxaboro...

All inorganic perovskites quantum dots (PeQDs) have attracted much attention for used in thin film display applications and solid-state lighting applications, owing to their narrow band emission with high photoluminescence quantum yields (PLQYs), color tunability, and solution processability. Here, we fabricated low-driving-voltage and high-efficiency CsPbBr PeQDs light-emitting devices (PeQD-LEDs) using a PeQDs washing process with an ester solvent containing butyl acetate (AcOBu) to remove excess ligands from the PeQDs. The CsPbBr PeQDs film washed with AcOBu exhibited a PLQY of 42%, and a narrow PL emission with a full width at half-maximum of 19 nm. We also demonstrated energy level alignment of the PeQD-LED in order to achieve effective hole injection into PeQDs from the adjacent hole injection layer. The PeQD-LED with AcOBu-washed PeQDs exhibited a maximum power efficiency of 31.7 lm W and EQE of 8.73%. Control of the interfacial PeQDs through ligand removal and energy level alignment in the device structure are promising methods for obtaining high PLQYs in film state and high device efficiency.

Recent developments in the field of p-conjugated polymers have led to considerable improvements in the performance of solution-processed organic light-emitting devices (OLEDs). However, further improving efficiency is still required to compete with other traditional light sources. Here we demonstrate efficient solution-processed multilayer OLEDs using small molecules. On the basis of estimates from a solvent resistance test of small host molecules, we demonstrate that covalent dimerization or trimerization instead of polymerization can afford conventional small host molecules sufficient resistance to alcohols used for processing upper layers. This allows us to construct multilayer OLEDs through subsequent solution-processing steps, achieving record-high power efficiencies of 36, 52 and 34 lm W À 1 at 100 cd m À 2 for solution-processed blue, green and white OLEDs, respectively, with stable electroluminescence spectra under varying current density. We also show that the composition at the resulting interface of solution-processed layers is a critical factor in determining device performance.

An ultra high efficiency blue organic light-emitting device using wide-energy-gap electron-transport material containing 3,5-dipyridylphenyl moieties and blue phosphorescent emitter, FIrpic, was developed. The optimized device showed extremely high power efficiencies of 56 lm/W (53 cd/A) at 100 cd/m2 and 42 lm/W (46 cd/A) at 1000 cd/m2 without light outcoupling enhancement.

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Three triphenyl benzene derivatives of 1,3,5‐tri(m‐pyrid‐2‐yl‐phenyl)benzene (Tm2PyPB), 1,3,5‐tri(m‐pyrid‐3‐yl‐phenyl)benzene (Tm3PyPB) and 1,3,5‐tri(m‐pyrid‐4‐yl‐phenyl)benzene (Tm4PyPB), containing pyridine rings at the periphery, are developed as electron‐transport and hole/exciton‐blocking materials for iridium(III) bis(4,6‐(di‐fluorophenyl)pyridinato‐N,C2′)picolinate (FIrpic)‐based blue phosphorescent organic light‐emitting devices. Their highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO) energy levels decrease as the nitrogen atom of the pyridine ring moves from position 2 to 3 and 4; this is supported by both experimental results and density functional theory calculations, and gives improved electron‐injection and hole‐blocking properties. They exhibit a high electron mobility of 10−4–10−3 cm2 V−1 s−1 and a high triplet energy level of 2.75 eV. Confinement of FIrpic triplet excitons is strongly dependent on the nitrogen atom position of the pyridine ring. The second exponential decay component in the transient photoluminescence decays of Firpic‐doped films also decreases when the position of the nitrogen atom in the pyridine ring changes. Reduced driving voltages are obtained when the nitrogen atom position changes because of improved electron injection as a result of the reduced LUMO level, but a better carrier balance is achieved for the Tm3PyPB‐based device. An external quantum efficiency (EQE) over 93% of maximum EQE was achieved for the Tm4PyPB‐based device at an illumination‐relevant luminance of 1000 cd m−2, indicating reduced efficiency roll‐off due to better confinement of FIrpic triplet excitons by Tm4PyPB in contrast to Tm2PyPB and Tm3PyPB.

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