Hong Tao

Efficient hybrid white organic light-emitting diodes with extremely long lifetime: the effect of n-type interlayer

The effect of n-type interlayer in hybrid white organic light-emitting diodes (WOLEDs) has been systematically investigated by using various n-type materials. A new finding, that the triplet energy rather than electron mobility or hole-blocking ability of interlayer plays a more positive role in the performance of hybrid WOLEDs, is demonstrated. Based on the new finding, a more efficient n-type interlayer bis[2-(2-hydroxyphenyl)-pyridine] beryllium has been employed to realize a high-performance hybrid WOLED. The resulting device (without n-doping technology) exhibits low voltages (i.e., 2.8 V for 1 cd/m2, 3.9 V for 100 cd/m2) and low efficiency roll-off (i.e., 11.5 cd/A at 100 cd/m2 and 11.2 cd/A at 1000 cd/m2). At the display-relevant luminance of 100 cd/m2, a total power efficiency of 16.0 lm/W, a color rendering index of 73 and an extremely long lifetime of 12596265 h are obtained. Such superior results not only comprehensively indicate that the n-type materials are effective interlayers to develop high-performance hybrid WOLEDs but also demonstrate a significant step towards real commercialization in WOLEDs.

Influence of source and drain contacts on the properties of the indium-zinc oxide thin-film transistors based on anodic aluminum oxide gate dielectrics

Thin-film transistors (TFTs) based on indium-zinc oxide (IZO) active layer and anodic aluminum oxide (Al2O3) gate dielectric layer were fabricated. The influence of source and drain (S/D) contacts on TFT performance was investigated by comparing IZO–TFTs with different S/D electrodes. The TFT with Mo S/D electrodes had higher output current and lower threshold voltage, but had poorer subthreshold swing and lower effective electron mobility compared to that with ITO S/D electrodes. By using x-ray photoelectron spectroscopy (XPS) depth profile analyzing method, it was observed that Mo was diffusing seriously into IZO, resulting in the variation of the effective channel length, thereby causing serious short-channel effect, poor subshreshold swing, and bad uniformity of the TFTs with Mo S/D electrodes.

Gate bias stress stability under light irradiation for indium zinc oxide thin-film transistors based on anodic aluminium oxide gate dielectrics

Thin-film transistors (TFTs) using indium zinc oxide as the active layer and anodic aluminium oxide (Al2O3) as the gate dielectric layer were fabricated. The device showed an electron mobility of as high as 10.1?cm2?V?1?s?1, an on/off current ratio of as high as ~108, and a turn-on voltage (Von) of only ?0.5?V. Furthermore, this kind of TFTs was very stable under positive bias illumination stress. However, when the device experienced negative bias illumination stress, the threshold voltage shifted to the positive direction. It was found that the instability under negative bias illumination stress (NBIS) was due to the electrons from the Al gate trapping into the Al2O3 dielectric when exposed to the illuminated light. Using a stacked structure of Al2O3/SiO2 dielectrics, the device became more stable under NBIS.

High-Performance Hybrid White Organic Light-Emitting Diodes Comprising Ultrathin Blue and Orange Emissive Layers

Two novel high-performance hybrid white organic light-emitting diodes have been realized by the delta-doping method. The device comprising a single ultrathin emissive layer exhibits a luminance of 46923 cd/m2 and a low efficiency roll-off. To further simplify the device structures, another device comprising double ultrathin emissive layers achieves low driving voltages, a high color rendering index (75), and a high efficiency (8.9 lm/W). Moreover, it is found that these two devices not only exhibit fairly pure white emission but also show a rather stable color. Such superior properties reveal that the utilization of delta-doping technology provides a new way to achieve high-performance devices.

Method for Fabricating Amorphous Indium-Zinc-Oxide Thin-Film Transistors With Copper Source and Drain Electrodes

We revealed a novel method to fabricate amorphous indium-zinc-oxide (a-IZO) thin-film transistors (TFTs) with inverted staggered back-channel-etch structure and copper (Cu) source/drain (S/D) electrodes. In particular, a gray-tone mask was used to define the S/D electrodes and active layer. The a-IZO layer acted not only as the active layer but also as the adhesive layer of Cu electrodes due to the good adhesion between Cu and a-IZO films. The presented TFTs exhibited a high saturated mobility of 12.2 cm2/Vs, a threshold voltage of -0.4 V, and a low subthreshold swing of 0.22 V/decade. The good electrical performance and reliability were attributed to the good contact property between Cu electrodes and a-IZO layer and very little Cu atoms diffusing into the channel layer.

Improvement of Mobility and Stability in Oxide Thin-Film Transistors Using Triple-Stacked Structure

In this letter, amorphous indium-zinc-oxide thin film transistors (α-IZO TFTs) with a multilayered structure of an active layer were investigated by embedding a different indium-content layer: 1) the low-indium layer contacted with dielectric to reduce defect states and block off the drift of photoinduced holes and 2) the high indium layer to provide a conductive path with reducing scattering centers. In the multilayered structure, the α-IZO TFTs with high mobility and good photoinduced stability could be achieved. The fabricated TFT exhibited a field-effect mobility of 50.4 cm2/Vs, which is thrice that of the single-layer device, an appropriate threshold voltage of 0.31 V, a low subthreshold swing of 0.14 V/decade, and a good negative bias illumination temperature stresses stability.

Properties-Adjustable Alumina-Zirconia Nanolaminate Dielectric Fabricated by Spin-Coating

In this paper, an alumina-zirconia (Al2O3-ZrO2) nanolaminate dielectric was fabricated by spin-coating and the performance was investigated. It was found that the properties of the dielectric can be adjusted by changing the content of Al2O3/ZrO2 in nanolaminates: when the content of Al2O3 was higher than 50%, the properties of nanolaminates, such as the optical energy gap, dielectric strength (Vds), capacitance density, and relative permittivity were relatively stable, while the change of these properties became larger when the content of Al2O3 was less than 50%. With the content of ZrO2 varying from 50% to 100%, the variation of these properties was up to 0.482 eV, 2.12 MV/cm, 135.35 nF/cm2, and 11.64, respectively. Furthermore, it was demonstrated that the dielectric strength of nanolaminates were influenced significantly by the number (n) of bilayers. Every increment of one Al2O3-ZrO2 bilayer will enhance the dielectric strength by around 0.39 MV/cm (Vds ≈ 0.86 + 0.39n). This could be contributed to the amorphous alumina which interrupted the grain boundaries of zirconia.