Publications (46) View all
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Article: A Highly Transparent Low Resistance ZnO/Ag Nanowire/ZnO Composite Electrode for Thin Film Solar Cells.
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ABSTRACT: We present an indium-free transparent conducting composite electrode composed of silver nanowires (AgNWs) and ZnO bi-layers. The AgNWs form a random percolating network embedded between the ZnO layers. The unique structural features of our ZnO/AgNW/ZnO multilayered composite allow for a novel transparent conducting electrode with unprecedented excellent thermal stability (~ 375(o)C), adhesiveness, and flexibility as well as high electrical conductivity (~ 8 Ω/sq) and good optical transparency (> 91% at 550 nm). Cu(In,Ga)(S,Se)(2) (CIGSSe) thin film solar cells incorporating this composite electrode exhibited a 20% increase of the power conversion efficiency compared to a conventional sputtered indium tin oxide-based CIGSSe solar cell. The ZnO/AgNW/ZnO composite structure enables effective light transmission and current collection as well as a reduced leakage current, all of which lead to better cell performance.ACS Nano 01/2013; · 10.77 Impact Factor -
Article: Enhanced performance of solution-processed amorphous LiYInZnO thin-film transistors.
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ABSTRACT: Solution-processed, amorphous lithium-doped YInZnO (L-YIZO) thin-film transistors (TFTs) are investigated. An appropriate amount of Li doping significantly enhances the field-effect mobility in TFT performance (~15 times greater than that of nondoped YIZO) without controlled annealing under water vapor or O(3)/O(2) environments. The addition of Li into solution-processed YIZO semiconductors leads to improved film quality, which results from enriched metal oxygen bonding and reduced defect sites, such as oxygen vacancies and hydroxyl groups. Li doping of an amorphous ionic oxide semiconductor (AIOS) could serve as an effective strategy for low-temperature and high-performance solution-processed AIOS TFTs.ACS Applied Materials & Interfaces 02/2012; 4(3):1456-61. · 4.53 Impact Factor -
Article: All solution-processed, fully transparent resistive memory devices.
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ABSTRACT: We fabricated all-solution processed, fully transparent resistive random access memory (sol-TRRAM) with a configuration of ITO/GaZnO(GZO)/ITO. All layers, including an active layer and top and bottom ITO electrodes, were deposited on a glass substrate by either spin coating or inkjet printing using a sol-gel solution. Our sol-TRRAM was transparent, with 86.5% transmittance at 550 nm. An initial forming process is unnecessary for the production of transparent memory due to the presence of sufficient inherent nonlattice oxygen ions in the solution-processed GZO layer. The sol-TRRAM also showed reasonable bipolar resistance switching with a low operation current (<100 μA) and excellent cycle endurance properties (>300 cycles). The main conduction mechanism during the set process can be explained by the trap-controlled space-charge limited conduction, and the resistance change occurred by the modification of the potential barrier height because of the charge injection by Fowler-Nordheim tunneling.ACS Applied Materials & Interfaces 11/2011; 3(11):4525-30. · 4.53 Impact Factor -
Article: Effect of carboxylic acid on sintering of inkjet-printed copper nanoparticulate films.
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ABSTRACT: The reduction effect of various carboxylic acids on inkjet-printed copper film was investigated. Carboxylic acids were exposed to the film by nitrogen gas that was bubbled through the liquid acids during the annealing process. It was observed that in the case of saturated monocarboxylic acid (formic, acetic, propionic, butyric), the acids with shorter hydrocarbon chains perform better in reducing the surface copper oxides in the printed copper conductive film. The printed films exposed to formic acid vapor exhibited the lowest resistivity (3.10 and 2.30 μΩ cm when annealed at 200 and 250 °C, respectively). In addition, the oxalic acid more effectively reduces copper oxide than formic acid and its usage can shorten the annealing time for highly conductive printed copper film. This reductive annealing process allows fabrication of copper patterns with low resistivity, (3.82 μΩ cm annealed at 250 °C) comparable to the resistivity of bulk copper.ACS Applied Materials & Interfaces 06/2011; 3(7):2377-82. · 4.53 Impact Factor -
Article: Influences of pH and ligand type on the performance of inorganic aqueous precursor-derived ZnO thin film transistors.
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ABSTRACT: The aqueous precursor-derived ZnO semiconductor is a promising alternative to organic semiconductors and amorphous silicon materials in applications requiring transparent thin-film transistors at low temperatures. The pH in the aqueous solution is an important factor in determining the device performance of ZnO-TFTs. Using a basic aqueous solution, the ZnO transistor annealed at 150 °C exhibited a high field-effect mobility (0.42 cm(2) V(-1) s(-1)) and an excellent on/off ratio (10(6)). In contrast, the ZnO layer annealed at 150 °C prepared from an acidic solution was inactive. Chemical and structural analyses confirmed that the variation of the device characteristics originates from the existing state difference of Zn in solution. The hydroxyo ligand is stable in basic conditions, which involves a lower energy pathway for the solution-to-solid conversion, whereas the hydrated zinc cation undergoes more complex reactions that occur at a higher temperature. Our results suggest that the pH and ligand type play critical roles in the preparation of aqueous precursor-based ZnO-TFTs which demonstrate high performance at low temperatures.ACS Applied Materials & Interfaces 03/2011; 3(3):774-81. · 4.53 Impact Factor
