The poor photovoltaic performance of state‐of‐the‐art blends of poly[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl] (PTB7) and [6,6]‐phenyl‐C61‐butyric acid (PCBM) at large active layer thicknesses is studied using space‐charge‐limited current mobility and photovoltaic device measurements. The poor performance is found to result from relatively low electron mobility. This is attributed to the low tendency of PTB7 to aggregate, which reduces the ability of the fullerene to form a connected network. Increasing the PCBM content 60–80 wt% increases electron mobility and accordingly improves performance for thicker devices, resulting in a fill factor (FF) close to 0.6 at 300 nm. The result confirms that by improving only the connectivity of the fullerene phase, efficient electron and hole collection is possible for 300 nm‐thick PTB7:PCBM devices. Furthermore, it is shown that solvent additive 1,8‐diiodooctane (DIO), used in the highest efficiency PTB7:PCBM devices, does not improve the thickness dependence and, accordingly, does not lead to an increase in either hole or electron mobility or in the carrier lifetime. A key challenge for researchers is therefore to develop new methods to ensure connectivity in the fullerene phase in blends without relying on either a large excess of fullerene or strong aggregation of the polymer.
12CaO‚7Al 2 O 3 electride (C12A7:e -) is a promising material for the cathode of organic light-emitting diodes (OLEDs), because it has a low work function (φ WF ) 2.4 eV), comparable to metal potassium, and good chemical/thermal stability in an ambient atmosphere. This study examines interfacial electronic structures between C12A7:eand tris-8-hydroxyquinoline aluminum (Alq 3 ) by ultraviolet photoelectron spectroscopy, finding that a low electron-injection barrier of 0.6 eV, which is approximately half of the value for the Al/LiF/Alq 3 interface with the lowest injection barrier, is achieved when the interface is formed on the C12A7:efilm surface obtained by using vacuum annealing and subsequent He plasma treatment. This treatment yields little change in the surface chemical composition and retains a low φ WF value (3.1 eV) of C12A7:e -. These results suggest that C12A7:ehas high potential as an efficient electron-injection electrode for OLEDs.
Carrier injection properties including threshold voltages of inverted top-emission organic light-emitting diodes (ITOLED) were improved by applying room temperature stable electride [Ca 24 Al 28 O 64 ] 4+ (4e -) (C12A7:e -), which has a low work function of ∼2.4 eV, and a p-type degenerated semiconductor Cu 2-x Se to bottom cathode and top anode buffer layers, respectively. The formation of a low-barrier electron injection contact between C12A7:eand tris(8-hydroxyqunoline)aluminum (Alq 3 ) is demonstrated by the current-voltage characteristics of electron-only devices, as well as by photoelectron spectroscopy. The threshold voltage of the ITOLED is reduced by changing the bottom cathode from Al to C12A7:efrom 9 to 7.6 V at 10 mA cm -2 . A 5 nm thick Cu 2-x Se top anode buffer layer, deposited at room temperature, reduced the threshold voltage further to ∼2 V. The luminance efficiency of ITOLED with a Cu 2-x Se buffer layer is nearly twice as large as that without the buffer layer. We emphasize that developing new electrode materials is an effective means to improve the performance of not only OLED but also other new optoelectronic devices.
The effects of O2 inductively coupled plasma (ICP) treatment on the chemical composition and work function of indium-tin-oxide (ITO) surface were investigated. Synchrotron radiation photoemission spectroscopy showed that the O2 ICP treatment resulted in the increase of the ITO work function by 0.8 eV. Incorporation of oxygen atoms near the ITO surface during the ICP treatment induced a peroxidic ITO surface, increasing the work function. The enhanced oxidation of a thin Ni overlayer on the O2-ICP-treated sample suggests that preventing the migration of oxygen atoms into the active region of organic light-emitting diodes is important for improving device lifetime.
We report the change of surface electronic structure of indium–tin–oxide (ITO) as a function of ultraviolet (UV)–ozone treatment time. The voltage of organic light emitting diodes at a current density of 100 mA/cm2 was reduced as the surface treatment time using UV–ozone was lengthened. X-ray photoelectron spectroscopy results showed that the relative concentration of carbon atoms decreased, but oxygen concentration increased relatively with UV–ozone treatment. This led to the increase in the ITO work function via the reduction of operation voltage.
The availability of 3D dental model scanning technology, combined with the ability to register CBCT data with digital models, has enabled the fabrication of orthognathic surgical CAD/CAM designed splints, customized brackets, and indirect bonding systems. In this study, custom lingual orthodontic appliances were virtually designed by merging 3D model images with lateral and posterior-anterior cephalograms. By exporting design information to 3D CAD software, we have produced a stereolithographic prototype and converted it into a cobalt-chrome alloy appliance as a way of combining traditional prosthetic investment and cast techniques. While the bonding procedure of the appliance could be reinforced, CAD technology simplified the fabrication process by eliminating the soldering phase. This report describes CAD/CAM fabrication of the complex anteroposterior lingual bonded retraction appliance for intrusive retraction of the maxillary anterior dentition. Furthermore, the CAD/CAM method eliminates the extra step of determining the lever arm on the lateral cephalograms and subsequent design modifications on the study model.
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