Highly transparent conductive, aluminum-doped zinc oxide (ZnO:Al) films were deposited on glass substrates by midfrequency magnetron sputtering of metallic aluminum-doped zinc target. ZnO:Al films with surface work functions between 3.7 and 4.4 eV were obtained by varying the sputtering conditions. Organic light-emitting diodes (OLEDs) were fabricated on these ZnO:Al films. A current efficiency of higher than 3.7 cd/A, was achieved. For comparison, 3.9 cd/A was achieved by the reference OLEDs fabricated on commercial indium-tin-oxide substrates
By using bathophenanthroline (BPhen) as an exciton blocking layer (EBL) at the organic/cathode contact of a standard copper phthalocyanine/C60 organic photovoltaic (OPV) device, power conversion efficiency was substantially increased from 0.86% to 2.64%. The BPhen-based devices showed a 45% increase in power conversion efficiency over that of an equivalent device with an EBL of bathocuproine. The performance improvement was analyzed in terms of the electron energy levels, optical transparencies and electron mobilities of the two EBLs. Based on these results, the roles of and requirements for an effective EBL were discussed. Combining the use of BPhen and a WO3 anodic buffer layer further increased the power conversion efficiency of the OPV device to 3.33%.
A series of bipolar phenanthroimidazole
derivatives, TTP-TPI, DPT-TPI,
and DPF-TPI, were designed and synthesized by incorporating polyaromatic
hydrocarbon groups to phenanthroimidazole through a phenyl bridge.
The bulky polyaromatic hydrocarbon units endow the molecules with
high glass-transition temperatures, nonplanar twisty structures which
reduce molecular aggregations. The bipolar transporting natures of
these materials are demonstrated by single-carrier devices with supported
of theoretical calculations. Nondoped organic light-emitting devices
(OLEDs) using these phenanthroimidazole derivatives as emitters show
blue-violet to sky-blue emissions with Commission Internationale de
l’Eclairage (CIE) coordinates of (0.16, 0.05) for TTP-TPI,
(0.16, 0.07) for DPT-TPI, and (0.17, 0.24) for DPF-TPI. The TTP-TPI-,
DPT-TPI-, and DPF-TPI-based nondoped devices show impressive external
quantum efficiencies (EQE) of 5.02, 5.25, 4.85%, respectively (corresponding
current efficiencies: 2.10, 3.13, and 8.41 cd/A). These values are
the best or among the best comparing to those of the reported nondoped
OLEDs with the corresponding color gamuts. These devices also show
small efficiency roll-off at high brightness (1000 cd/m2) with EQEs drop by 20.7, 12, and 0%. Moreover, with well-balanced
carrier transport, DPF-TPI based device can achieve a higher brightness
of 10000 cd/m2 with EQE maintaining at 4.49% (only drop
by 7.4%).
Naphthyl-linked donor–π–acceptor fluorophores were utilized to achieve high performance and good color purity violet-blue emission in organic light-emitting devices (OLEDs).
A bilayer connection unit of Mg-doped Alq3 and F4-TCNQ-doped m-MTDATA was investigated for application in stacked organic light-emitting device. This connection unit led to a stacked OLED with a luminous efficiency twice that of a single-unit OLED. Electronic structures, including relevant electron energy levels, of the various interfaces in the stacked OLED were studied by using ultraviolet photoemission spectroscopy and used to discuss the working mechanisms of the stacked OLED. The p-type dopant F4-TCNQ was shown to induce a large band bending of 1.36eV and facilitates efficient carrier injection from the connection units into the carrier-transporting layers.
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