title: Hierarchical weeping willow nano-tree growth and effect of branching on dye-sensitized solar cell efficiency.
abstract: In this paper we have demonstrated the simple, low cost, low temperature, hydrothermal growth of weeping willow ZnO nano-trees with very long branches to realize high efficiency dye-sensitized solar cells (DSSCs). We also discuss the effects of branching on solar cell efficiency. By introducing branched growth on the backbone ZnO nanowires (NWs), the short circuit current density and the overall light conversion efficiency of the branched ZnO NW DSSCs increased to almost four times that for vertically grown ZnO NWs. The efficiency increase is attributed to the increase in surface area for higher dye loading and light harvesting and also to reduced charge recombination through direct conduction along the crystalline ZnO branches. As the length of the branches increased, the branches became flaccid and the increase in solar cell efficiency slowed down because the effective surface area increase was hindered by branch bundling during the drying process and subsequent decrease in the dye loading.
authors.affiliation: Applied Nano Technology and Science Lab, Department of Mechanical Engineering, KAIST, 373-1 Gusung-Dong, Yusong-Gu, Daejeon 305-701, Korea.
authors.forename: Indria
authors.initials: I
authors.lastname: Herman
authors.forename: Junyeob
authors.initials: J
authors.lastname: Yeo
authors.forename: Sukjoon
authors.initials: S
authors.lastname: Hong
authors.forename: Daeho
authors.initials: D
authors.lastname: Lee
authors.forename: Koo Hyun
authors.initials: KH
authors.lastname: Nam
authors.forename: Jun-ho
authors.initials: JH
authors.lastname: Choi
authors.forename: Won-hwa
authors.initials: WH
authors.lastname: Hong
authors.forename: Dongjin
authors.initials: D
authors.lastname: Lee
authors.forename: Costas P
authors.initials: CP
authors.lastname: Grigoropoulos
authors.forename: Seung Hwan
authors.initials: SH
authors.lastname: Ko