The optical band gap of ZnO thin films deposited on fused quartz by metal-organic chemical-vapor deposition was studied. The optical band gap of as-grown ZnO blueshifted from $3.13\text{to}4.06\mathrm{eV}$ as the growth temperature decreased from $500\text{to}200°\mathrm{C}$ . After annealing, the optical band gap shifted back to the single-crystal value. All the ZnO thin films studied show strong band-edge photoluminescence. X-ray diffraction measurements showed that samples deposited at low temperatures $(<450°\mathrm{C})$ consisted of amorphous and crystalline phases. The redshift of the optical band gap back to the original position after annealing was strong evidence that the blueshift was due to an amorphous phase. The unshifted photoluminescence spectra indicated that the luminescence was due to the crystalline phase of ZnO, which was in the form of nanocrystals embedded in the amorphous phase.

Single crystal zinc oxide nanocombs were synthesized in bulk quantity by vapor phase transport. A glucose biosensor was constructed using these nanocombs as supporting materials for glucose oxidase $\left({\mathrm{GO}}_x\right)$ loading. The zinc oxide nanocomb glucose biosensor showed a high sensitivity $(15.33\mu \mathrm{A}∕{\mathrm{cm}}^2\mathrm{mM})$ for glucose detection and high affinity of ${\mathrm{GO}}_x$ to glucose (the apparent Michaelis-Menten constant $K_M^{\mathrm{app}}=2.19\mathrm{mM}$ ). The detection limit measured was $0.02\mathrm{mM}$ . These results demonstrate that zinc oxide nanostructures have potential applications in biosensors.

We reported an efficient inverted bulk-heterojunction [regioregular of poly(3-hexylthiophene): (6,6)-phenyl ${\text{C}}_{61}$ butyric acid methyl ester] solar cell with a highly transparent sol-gel derived ZnO film as electron selective layer and ${\text{MoO}}_3$ as hole selective layer. By modifying the precursor concentration of sol from 0.75 to $0.1M$ , the optical transmittance of ZnO film increases from 75% to 95%. This improvement in transmittance increases the short-circuit density of inverted solar cell from 5.986 to $8.858\text{mA}/{\text{cm}}^2$ without sacrificing the open-circuit voltage and fill factor of the device. We also demonstrated that the device incorporated with ${\text{MoO}}_3$ has a larger open-circuit voltage and fill factor than the device without ${\text{MoO}}_3$ . Power conversion efficiency of 3.09% was achieved under simulated AM 1.5G illumination of $100\text{mW}/{\text{cm}}^2$ .

In this letter, the authors report a dye-sensitized solar cell (DSSC) using a ZnO-nanoflower film photoanode, which was grown by a hydrothermal method at $95°\mathrm{C}$ . The dye used was cis-bis(isothiocyanato)bis($2,2^{\prime }$ -bipyridyl-$4,4^{\prime }$ -dicarboxylato)-ruthenium(II) bis-tetrabutylam-monium ($N$ -719). At AM1.5G irradiation with $100\mathrm{mW}∕{\mathrm{cm}}^2$ light intensity, the DSSC based on ZnO-nanoflower film showed an energy conversion efficiency of 1.9%, which is much higher compared to that (1.0%) of the control device constructed using a photoanode of upstanding ZnO-nanorod array fabricated by hydrothermal method as well. The better performance of ZnO-nanoflower DSSC was due to a better dye loading and light harvesting of the ZnO-nanoflower film. The results demonstrate potential application of ZnO-nanoflower array for efficient dye-sensitized solar cells.