Preparation Of Un-doped And Aluminum Doped Zinc Oxide Nanostructures And Their Application To Dye-sensitized Solar Cell

Zinc oxide is an n-type semiconductor and it has a large band gap (3.3 - 3.6 eV), and large exciton binding energy of 60 meV at room temperature, which yields efficient luminescence at room temperature. Also ZnO shows both photoconductivity and photocatalystic activity. ZnO is one of the most promising candidates for nanodevices and suggests a great deal of possible practical applications for light-emitting diodes, photodiodes, wave guide devices, gas sensors and solar cells. Furthermore aluminum-doped zinc oxide (AZO) films show the lowest electrical resistivity of 2.4×10^-4Ω-cm, which is similar to that of ITO films. AZO films are wide band gap semiconductors ( E_g= 3.4-3.9 eV), which show good optical transmission in the visible and near-infrared (1R) regions. Also AZO films are nontoxic, inexpensive, and easy to fabricate and have a high stability in hydrogen plasma. Due to these unique properties, AZO films have been used as transparent conducting electrodes in solar cells.Recent experimental verifications of predicted ZnO nanostructures have increased their attractiveness as promising candidates for optoelectronic and spin electronics based devices. A control over dopant speciation and the determination of the size-dependence of functional properties at the nanoscale become then indispensable.We present here the results of our current efforts on:1. ZnO nanoparticles of different sizes were prepared by hydrothermal method. The effect of polyethylene pyrrolidone (PVP) addition on the particles size has been studied. ZnO nanosheets and nanorods were obtained by heat-treatment of ZnO nanoparticles for different duration. TEM, XRD and SEM were used to investigate the particles sizes, the particles shapes and the transformation process.2. Well dispersed and small sized (about 5 nm in diameter) ZnO nanoseeds were prepared. Single crystalline Al doped ZnO (AZO) nanorods with length varies from 550 nm to 800 nm and average diameter ranging from 70 nm to 100 nm have been synthesized by wet chemical method. Transmission electron microscopy (TEM) images indicated that the nanorods have the same crystalline structure and growth direction. Also scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to investigate the morphology of products. The energy-dispersive-x-ray spectrometer (EDS) measurements ensured that ZnO nanorods crystal was doped with Al.3. Aluminum doped zinc oxide nanoparticles of about 40 nm in diameter were prepared by hydrothermal method. The phase and the morphology of the above nanoparticles were investigated by XRD, SEM and TEM. AZO films were fabricated. The UV-Vis absorption and transmittance of these films were studied. Also the electrical resistivities of these films were measured. A low resistivity of about 0.12Ω.cm was obtained.4. ZnO nanoparticles of 15 nm in diameter were prepared by hydrothermal method. ZnO nanosheets were obtained by re-hydrothermal treatment of ZnO nanoparticles.The phase and morphology were investigated by using TEM, SElvl and XRD. Also the UV-vis absorption of the fabricated thin films was studied. A fill factor of 0.55, short-circuit current of 2.059 mA/cm², open-circuit voltage of 0.593 V and an overall light to electricity conversion efficiency of 1.55 % for the solar cell based on ZnO nanosheets were obtained.