Yung-Der Juang

Improved Electrical and Thermal Stability of Solution-Processed Li-Doped ZnO Thin-Film Transistors

The effects of lithium (Li) doping on the performance of solution-processed zinc oxide (ZnO) thin-film transistors (TFTs) grown using the sol-gel method are investigated. Li-doped ZnO films as channel layers are chemically prepared by spin coating the gel with an aqueous solution of zinc acetate dihydrate, Li nitrate, and ethanolamine. TFT devices fabricated with 2 at.% Li-doped films show a good field-effect mobility of 3.31 cm2/V·s, a subthreshold slope of 0.82 V/dec, and an on-off current ratio of over 105. These TFT devices also show good thermal and electrical stability, which is mainly attributed to the compact surface morphology of the channel layer, small carrier concentration, and less oxygen deficiency, which reduces the interface electrical trapping at the gate insulator.

Antireflective and Radiation Resistant ZnO Thin Films for the Efficiency Enhancement of GaAs Photovoltaics

In this paper, zinc oxide (ZnO) thin films as an antireflective (AR) coating layer have been successfully fabricated on GaAs solar cells by the sol―gel method. ZnO films were prepared chemically by spin coating the gel with an aqueous solution of zinc acetate and ethanolamine. The current―voltage measurements of the solar cells confirmed the increase of the short-circuit current induced by the AR effect. The open-circuit voltage and fill factor were also improved by the surface passivation. As a result, the conversion efficiency of the cells without an AR coating (8.2%) was significantly enhanced to 13.6%. The results indicate that the chemical deposition of ZnO was effective for the AR coating of GaAs solar cells. Additionally, we demonstrate that the cells coated with radiation resistant ZnO films exhibit less efficiency decay than the devices without such treatment. Under the maximum proton fluence of 10 13 cm ―2 , the conversion efficiency decay was reduced to 69.8%, while the solar cells without ZnO films showed an efficiency decay of 83.1%.

Transparent Conducting Ti-Doped ZnO Thin Films Applied to Organic Light-Emitting Diodes

Transparent Ti-doped zinc oxide (TZO) thin films with high conductivity were fabricated using radio frequency (rf) magnetron sputtering on glass substrates. The material properties of the TZO films correlated with sputtering parameters were discussed. The TZO thin films with thickness of 258.5-nm-thick were used as anodes of organic light emitting diode devices and the devices exhibited lower turn-on voltage (3 V) and higher current efficiency than the commercial indium tin oxide (ITO) anodes. The TZO thin film may be a potential alternative to an ITO anode due to its low operating voltage, low price, and non-toxicity.

Effect of ZnO Buffer Layer on the Bending Durability of ZnO:Ga Films Grown on Flexible Substrates: Investigation of Surface Energy, Electrical, Optical, and Structural Properties

ZnO:Ga (GZO) transparent conducting oxide (TCO) films are deposited on flexible polyethersulfone (PES) substrates using the radio frequency sputtering technique. The bending durability of flexible TCOs is improved by inserting 100-nm-thick ZnO buffer layers. The strain of the samples with and without buffer layers arising from bending is studied using X-ray diffraction. After the insertion of 100-nm-thick ZnO buffer layers, the strain of GZO films without ZnO after outward and inward bending for 2000 cycles decreases from 2.063 ×10-3 and 2.203 × 10-3 to 1.74 × 10-3 and 1.966 × 10-3, respectively. Such strain variation is caused by the difference in adhesive force at the surface of 100-nm-thick ZnO/PES and PES. The surface energy of PES and 100-nm-thick ZnO/PES bent outwards and inwards for 2000 cycles increased from 34.38 and 30.56 to 36.45 and 36.03 mJ/m2, respectively.

The effects of ultraviolet-ozone-treated ultra-thin MnO-doped ZnO film as anode buffer layer on the electrical characteristics of organic light-emitting diodes

In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing an MnO-doped ZnO film as a buffer layer between the indium tin oxide (ITO) electrode and the α-naphthylphenylbiphenyldiamine hole transport layer. The enhancement mechanism was systematically investigated, and the X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results revealed the formation of the UV-ozone-treated MnO-doped ZnO film. With this film, the work function increased from 4.8 eV (standard ITO electrode (∼ 10±5 Ω/◻)) to 5.27 eV (UV-ozone-treated MnO-doped ZnO deposited on the ITO electrode with 1 wt. % for 1 nm), while the surface roughness of the UV-ozone-treated MnO-doped ZnO film was smoother than that of the ITO electrode. The deposited UV-ozone-treated MnO-doped ZnO film increased the surface energy and polarity of the ITO surface, as determined from contact angle measurements. Further, results from admittance spectroscopy showed that the inserted UV-ozone-treated Mn...