The authors report the very high luminous efficiency in solution processed red electrophosphorescent organic light emitting devices using small molecular host and guest materials. The maximum luminous efficiency reached 12.7cd∕A, corresponding to external quantum efficiency of 15.1%, with its emission peak wavelength of 620nm and the Commission Internationale de l’Eclairage coordinates of (0.65, 0.33). Along with these excellent performances of the solution processed device, which were comparable to those of the vacuum deposited counterpart device with similar structure and materials, the comparative study on both devices suggests the merits of the solution process adopting robust small molecular materials only.

A novel host material containing silicon‐cored spirobifluorene derivative (SBP‐TS‐PSB), is designed, synthesized, and characterized for red phosphorescent organic light‐emitting diodes (OLEDs). The SBP‐TS‐PSB has excellent thermal and morphological stabilities and exhibits high electroluminescence (EL) efficiency as a host for the red phosphorescent OLEDs. The electrophosphorescence properties of the devices using SBP‐TS‐PSB as the host and red phosphorescent iridium (III) complexes as the emitter are investigated and these devices exhibit higher EL performances compared with the reference devices with 4,4′‐N,N′‐dicarbazole‐biphenyl (CBP) as a host material; for example, a (piq)2Ir(acac)‐doped SBP‐TS‐PSB device shows maximum external quantum efficiency of ηext = 14.6%, power efficiency of 10.3 lm W−1 and Commission International de L'Eclairage color coordinates (0.68, 0.32) at J = 1.5 mA cm−2, while the device with the CBP host shows maximum ηext = 12.1%. These high performances can be mainly explained by efficient triplet energy transfer from the host to the guests and improved charge balance attributable to the bipolar characteristics of the spirobifluorene group.

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There has been growing interest in organic thin-film transistors (OTFTs) because of their potential applications in flexible, low-cost integrated circuits, such as smart cards, RF identification tags, and display backplanes, such as liquid crystal displays, electronic paper, and organic electroluminescent displays. [1,2] In particular, since organic semiconductors based on polymers and oligomers are attractive for their easy solution processing for film formation, recent research on OTFTs has been more focused on flexible electronic devices/display applications. Therefore, the most desired ultimate goal of organic semiconductor devices is to realize flexible electronics and displays that can be processed through all-solution processes including deposition of the active organic layers, the gate insulators, and the electrodes. Here we demonstrate all-solutionprocessed n-type organic transistors for the first time by depositing the source and drain metal by a spinning metal process.Despite the great interest and progress in organic and polymeric TFTs, most of the high field-effect-mobility OTFTs have been based on p-type channel materials. However, even if n-channel semiconducting materials are important for making ambipolar transistors [3,4] and complementary circuits, [5] they are relatively rare compared with the p-type materials. The reported field-effect mobilities of n-type OTFTs to date also show lower values than those of p-type devices. In addition, it has usually been observed that the solution-processed OTFTs show poorer performance than the vacuum-processed devices: for example, although the vacuum-evaporated pentacene transistor has shown high field-effect hole mobilities exceeding 1 cm 2 V ±1 s ±1 , [6] the solution-processed p-type transistor using the pentacene precursor showed low fieldeffect mobilities below 0.1 cm 2 V ±1 s ±1 . [7] Reports about the solution-processed n-type transistors are also relatively rare [5,8±10] and they usually show low charge-carrier mobilities (~10 ±2 cm 2 V ±1 s ±1 or less) [5,8,10,11] except that most recently the observation of a field-effect electron mobility as high as 0.1 cm 2 V ±1 s ±1 for a solution spin-coated conjugated ladder polymer was reported.[9] Here we report on solution-processed n-type OTFTs with high field-effect mobilities, based on the soluble derivatives of fullerene (C 60 ) as n-type channel materials. We obtained high field-effect electron mobilities of 0.02±0.1 cm 2 V ±1 s ±1 depending on the work-function of the source and drain metals, demonstrating that the electron injection current is contact-limited because of the Schottky barrier at the contact. Furthermore, we fabricated n-type OTFTs by an all-solution-deposition process including source and drain metals as well as gate insulators and organic semiconductors. These types of OTFTs are well suited for a wide range of existing and future flexible circuits and display applications that require a simplified production process and low-weight and low-cost products. In order to achieve the solu...

The syntheses of the bright deep blue emitting mixed ligand Ir(III) complexes comprising two cyclometalating, one phosphine and one cyano, ligands are reported. In this study, a firm connection between the nature of the excited states and the physicochemical behavior of the complexes with different ligand systems is elucidated by correlating the observed crystal structures, spectroscopic properties, and electrochemical properties with the theoretical results obtained by the density functional theory (DFT) methods. The cyclometalating ligands used here are the anions of 2-(4',6'-difluorophenyl)-pyridine (F2ppy), 2-(4',6'-difluorophenyl)-4-methyl pyridine (F2ppyM), and 4-amino-2-(4',6'-difluorophenyl)-pyridine (DMAF2ppy). The phosphine ligands are PhP(O-(CH2CH2O)3-CH3)2 and Ph2P(O-(CH2CH2O)n-CH3), where Ph = phenyl and n = 1 (P1), 3 (P3), or 8 (P350). The thermal stabilities of the complexes were enhanced upon increasing the "n" value. The crystal structures of the complexes, [(DMAF2ppy)2Ir(P1)CN], (P1)DMA, and [(F2ppyM)2Ir(P3)CN], (P3)F2M, show the cyano and phosphine groups being in a cis configuration to each other and in a trans configuration to the coordinating Cring atoms. The long Ir-Cring bond lengths are ascribed to the trans effect of the strong phosphine and cyano ligands. DFT calculations indicate that the highest occupied molecular orbital (HOMO) is mainly contributed from the d-orbitals of the iridium atom and the pi-orbitals of cyclometalating and cyano ligands, whereas the lowest unoccupied molecular orbital (LUMO) spreads over only one of the cyclometalating ligands, with no contribution from phosphine ligands to both frontier orbitals. Dimethylamino substitution increases the energy of the emitting state that has more metal-to-ligand-charge-transfer (MLCT) character evidenced by the smaller vibronic progressions, smaller difference in the 1MLCT and 3MLCT absorption wavelengths, and higher extinction coefficients (epsilon) than the F2ppy and F2ppyM complexes. However, the increase in the basicity of the dimethylamino group in the DMAF2ppy complexes in the excited states leads to distortions and consequent nonradiative depopulation of the excited states, decreasing their lower photoluminescence (PL) efficiency. The effect of the substituents in the phosphine ligand is more pronounced in the electroluminescence (EL) than in the PL properties. Multilayer organic light emitting devices (OLEDs) are fabricated by doping the Ir(III) complexes in a blend of mCP (m-bis(N-carbazolyl benzene)) and polystyrene, and their device characteristics are studied. The (P3)F2M complex shows a maximum external quantum efficiency (etaex) of 2%, a maximum luminance efficiency (etaL) of 4.13 cd/A at 0.04 mA/cm2, and a maximum brightness of 7200 cd/m2 with a shift of the Commission Internationale de L'Eclairage (CIE) coordinates from (0.14, 0.15) in film PL to (0.19, 0.34) in EL.