Study On Dye-sensitized Solar Cells Based On ZnO Branched Nanostructure Arrays

Dye-sensitized solar cells (DSCs) are considered to be a promising alternative to con-ventional silicon solar cells due to their properties of high conversion efficiency and low cost. A semiconductor film is one of the key parts which determine the conversion efficiency of a dye-sensitized solar cell. In this paper, we intend to firstly prepare ZnO nanorod arrays grown directly on the conducting glass substrates and then synthesize branches grown on the fix fac-ets of every nanorod to construct ZnO branched nanorod arrays by taking advantages of the preferential adsorption of structure directing agents on different facets of hexagonal ZnO crystals, which aims at not only keeping the good electron transport but also increasing the surface area of nanorod arrays, resulting in the improvement of conversion efficiency.Dense ZnO branched nanorod arrays were synthesized via the two-step solution method, which the mixture solution of Zn(NO₃)₂·6H₂O and HMT was used as the growth system. Firstly, ZnO nanorod arrays were vertically grown on the conducting glass substrate, and then the branches were grown on the six facets of every nanorod by adding 1, 3- diaminopropane (DAP) in the solution as the structure directing agent. The microstructures of the ZnO branched nanorod arrays were characterized by scanning electron microscopy (SEM). The absorption ability for N719 dye was evaluated by measuring the amount of dye absorbed on the films. The effects of the seed film, the concentration of the first and secondary growth so-lution, the growth mode and the additives on the diameter, length and distribution density of the ZnO nanostructures were investigated.The ZnO branched nanorods with good dye absorption ability was obtained under the following experimental conditions: without seed film; the concentration of the first growth solution was 0.03 M; the concentration of the secondary growth solution was 0.05M; the concentration of the DAP was 0.08M; the first growth temperature was 90℃; the first growth time was 6 h; the second growth temperature was 60℃; the total second growth time was 6 h with refreshing new solution every 2 h. The ZnO branched nanorod array film prepared under the optimal conditions were characterized by XRD, PL, EDS and UV-vis, The dye-sensitized solar cell based on the optimized branched ZnO nanorod arrays reached 1.66 % in conversion efficiency. Furthermore,we tried to cover the ZnO branched nanorod array with different TiO₂ layers, and sensitized the TiO₂ covered ZnO branched nanorod arrays with N719 and P3HT/PCBM, respectively. The potocurrent-voltage performances of these DSCs based on ZnO/TiO₂ nanostructures were evaluated.