Jenn-Ming Wu

Efficient electron transport in tetrapod-like ZnO metal-free dye-sensitized solar cells

The tetrapod-like ZnO nanopowders are employed to construct an efficient electron transport network as the photoanode of the dye-sensitized solar cells (DSCs). Due to the high extinction coefficient of the metal-free D149 dye offering a high photocurrent through the ZnO network, the best performance of DSCs based on a 42 µm terapod-like ZnO film showed a high energy conversion efficiency of 4.9% with a high short-circuit photocurrent density of 12.3 mA cm−2, an open-circuit photovoltage of 0.6 V, and a fill factor of 0.65 under AM 1.5 irradiation. Highly efficient electron transport may also be ascribed by a long effective electron diffusion length of 46 µm determined from the electrochemical impedance spectroscopy which is consistent with thickness dependent JSC measurements.

Improved performance of flexible dye-sensitized solar cells by introducing an interfacial layer on Ti substrates

The recombination reaction of injected electrons with triiodide ion in the electrolyte limits the efficiency of dye-sensitized solar cells (DSSCs). This study reports the preparation of a sponge-like and conformal TiO2 underlayer by hydrogen peroxide oxidation of Ti foil. This underlayer serves as a charge recombination barrier layer at the nanocrystalline TiO2/substrate interface, and suppresses the recombination reaction. This sponge-like TiO2 underlayer increases the electrical contact area between the Ti substrate and nanocrystalline TiO2, helping nanocrystalline TiO2 attach to the Ti substrate. This study compares the performance of DSSCs that were subjected to different Ti surface treatments. Electrochemical impedance spectroscopy results confirm that the proposed sponge-like TiO2 underlayer increased the open-current voltage (VOC) and fill factor (FF) due to prolonged electron life time (τeff), and minimized resistance at the TiO2/Ti interface (RCT). With an optimal thickness of nanocrystalline TiO2 and concentration of I2, we achieved a conversion efficiency of 6.75% for a back-illuminated DSSC.

Promising electron field emitters composed of conducting perovskite LaNiO3 shells on ZnO nanorod arrays

We report a semiconductor–perovskite composite system with promising field emission properties. The composite system was fabricated by sputtering perovskite LaNiO3 (LNO) shells on one dimensional (1D) well-aligned hydrothermally produced ZnO nanorod arrays (ZNAs). The ZNA–LNO core–shell hetero-structures were demonstrated to be much more efficient field emitters than ZNAs. Since the work function of LNO (4.5 eV) is lower than that of ZnO (5.3 eV), a shallow well is formed in thermal equilibrium in the ZNA–LNO heterojunction. When an electric field is applied, the produced well is of much benefit for the flow of electrons from the GZO seed layers through the ZNA to the LNO shells. Consequently, the emission of electrons into vacuum by tunneling is easily realized due to the low work function of the LNO coatings. Our 1D semiconductor–perovskite composite system provides a prospect for the development of practical field emission electron sources.

Facet‐Dependent Photocatalytic Activity and Facet‐Selective Etching of Silver(I) Oxide Crystals with Controlled Morphology

The shape of Ag2O crystals that evolve from edge and corner‐truncated cubes into rhombicuboctahedrons, then to hexapods can be conducted precisely by simply controlling the amount of AgNO3, NH4NO3 and NaOH precursors. The edge and corner‐truncated cube crystals possess the highest photocatalytic activity, followed by the rhombicuboctahedrons, then the hexapods. The photocatalytic activity of the Ag2O crystals depends greatly on the type of the exposed facets. The {1 0 0} facets exhibit the highest photocatalytic activity in methyl orange solution under full‐spectrum light irradiation, followed by the {1 1 0} facets, then the {1 1 1} facets. The {1 0 0} facets are also demonstrated to show intense susceptibility toward etching by NH3.

Opto-electrical properties and chemisorption reactivity of Ga-doped ZnO nanopagodas

ZnO nanostructures with Ga doping prepared by metal–organic chemical vapor deposition developed an interesting nanopagoda shape with exposed {111}, {112}, {201}, and {101} lateral planes instead of {100} and {110} in the usually observed ZnO nanorods or nanowires. The types of exposed planes strongly affect those properties relating to surface reactivity. In this work, we report the opto-electrical properties and chemical reactivity of the Ga-doped ZnO nanopagodas and ZnO nanowires. Ultraviolet responses of photodetectors demonstrated that Ga-doped ZnO nanopagodas not only possessed a faster electron–hole generation and recombination rate but also exhibited higher photocatalytic activities than the ZnO nanowires. The improved performance of Ga-doped ZnO nanopagodas is due to the enhanced O2 and H2O chemisorption reactivity of the {111}, {112}, {201}, and {101} planes relative to the {100} and {110} planes.

Extremely high efficient nanoreactor with Au@ZnO catalyst for photocatalysis

We fabricated a photocatalytic Au@ZnO@PC (polycarbonate) nanoreactor composed of monolayered Au nanoparticles chemisorbed on conformal ZnO nanochannel arrays within the PC membrane. A commercial PC membrane was used as the template for deposition of a ZnO shell into the pores by atomic layer deposition (ALD). Thioctic acid (TA) with sufficient steric stabilization was used as a molecular linker for functionalization of Au nanoparticles in a diameter of 10 nm. High coverage of Au nanoparticles anchored on the inner wall of ZnO nanochannels greatly improved the photocatalytic activity for degradation of Rhodamine B. The membrane nanoreactor achieved 63% degradation of Rhodamine B within only 26.88 ms of effective reaction time owing to its superior mass transfer efficiency based on Damköhler number analysis. Mass transfer limitation can be eliminated in the present study due to extremely large surface-to-volume ratio of the membrane nanoreactor.