Nanoforest of Hydrothermally Grown Hierarchical ZnO Nanowires for a High Efficiency Dye-Sensitized Solar Cell

TLDR

The study demonstrates that selectively growing high‑density, branched hierarchical ZnO nanowire “nanoforest” photoanodes can increase dye‑sensitized solar cell power‑conversion efficiency. A parametric hydrothermal synthesis combining lengthwise and branched growth, engineered seed particles, and capping polymer was used to optimize the hierarchical ZnO nanowire photoanodes. The nanoforest DSSCs achieved nearly fivefold higher light‑conversion efficiency than conventional upstanding ZnO nanowires, owing to greater surface area for dye loading and reduced charge recombination via direct conduction pathways.

Abstract

In this paper, in order to increase the power conversion efficiency we demonstrated the selective growth of "nanoforest" composed of high density, long branched "treelike" multigeneration hierarchical ZnO nanowire photoanodes. The overall light-conversion efficiency of the branched ZnO nanowire DSSCs was almost 5 times higher than the efficiency of DSSCs constructed by upstanding ZnO nanowires. The efficiency increase is due to greatly enhanced surface area for higher dye loading and light harvesting, and also due to reduced charge recombination by providing direct conduction pathways along the crystalline ZnO "nanotree" multi generation branches. We performed a parametric study to determine optimum hierarchical ZnO nanowire photoanodes through the combination of both length-wise growth and branched growth processes. The novel selective hierarchical growth approach represents a low cost, all solution processed hydrothermal method that yields complex hierarchical ZnO nanowire photoanodes by utilizing a simple engineering of seed particles and capping polymer.