AVS 51st International Symposium
    Nanometer-scale Science and Technology Thursday Sessions
       Session NS2-ThA

Paper NS2-ThA4
Growth Of ZnO Nanowires and Their Applications in Dye Sensitized Solar Cells

Thursday, November 18, 2004, 3:00 pm, Room 213D

Session: Nanowires II
Presenter: J.B. Baxter, University of California Santa Barbara
Authors: J.B. Baxter, University of California Santa Barbara
M. Reichman, University of Texas-Austin
E.S. Aydil, University of California Santa Barbara
Correspondent: Click to Email
ZnO is a wide band gap semiconductor (Eg = 3.37 eV) with applications in UV optoelectronics, varistors, piezoelectronics, and photovoltaics. Nanostructured ZnO can enable applications that require high semiconductor surface area such as sensors and dye sensitized solar cells. We have grown single crystal ZnO nanowires ~80 nm in diameter and several microns long by chemical vapor deposition (CVD) using the organometallic precursor zinc acetylacetonate (Zn(acac)@sub2@) in the presence of oxygen. Dense arrays of ZnO nanowires exhibit large surface areas and can be grown on various oxide substrates, making them suitable as the mesoporous semiconductor in dye sensitized solar cells. Single crystal ZnO nanowires offer improved conduction pathways compared to sintered nanoparticles used currently, where electron transport occurs by a hopping mechanism. The surface area for dye adsorption can be increased significantly by extending the growth time to allow for the nucleation and growth of smaller secondary nanowires from the primary nanowires, improving current densities in the cells. We have used these types of nanowires to produce initial solar cells with short circuit current densities of 75 µA/cm@super2@, open circuit voltages of 0.63 V, and fill factors of 39 % when illuminated with 100 mW/cm@super2@ simulated solar light. A limitation of the initial solar cells is poor light harvesting, with less than 10% of incident light absorbed by the dye. We are currently investigating methods for seeding nanowire growth to improve the nucleation density, which will increase nanowire surface area and dye adsorption. Transport properties of the nanowires can be significantly enhanced by treatment in hydrogen plasma at room temperature. H atoms passivate defects and increase conductivity by increasing carrier densities. H exposure improves the UV photoluminescence of the nanowires and both the fill factor and the open circuit voltage of the solar cells.