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

Seung Hwan Ko,Hyung Jin Sung,Koo Hyun Nam,Hyun Wook Kang,Suk Joon Hong,Costas P Grigoropoulos,Daeho Lee,Joon Yeob Yeo

doi:10.1021/nl1037962

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.

Highlights

Dye-sensitized solar cells (DSSCs) based on oxide semiconductors and organic dyes or metallorganic-complex dye have recently emerged as the most promising candidate systems to achieve efficient solar-energy conversion since they are flexible, inexpensive, and easier to manufacture than silicon solar cells.[1,2,3]
We report that “nanoforest” of high density, longbranched “treelike” multigeneration hierarchical ZnO NW photoanodes can significantly increase the power conversion efficiency
We performed parametric study to improve the efficiency of hierarchical ZnO NW photoanodes by combining length-wise growth (LG) and branched growth (BG)

Summary

Introduction

Dye-sensitized solar cells (DSSCs) based on oxide semiconductors and organic dyes or metallorganic-complex dye have recently emerged as the most promising candidate systems to achieve efficient solar-energy conversion since they are flexible, inexpensive, and easier to manufacture than silicon solar cells.[1,2,3] The. The efficiency increase is due to substantially enhanced surface area enabling higher dye loading and light harvesting and is due to reduced charge recombination by direct conduction along the crystalline ZnO nanotree multigeneration branches. High quality hierarchical branched ZnO NW forest can be grown only after both (1) removal of polymer (HMTA, PEI) by heating the ZnO NW and (2) coating with seed NPs on the backbone ZnO NW surface.

Results

Conclusion