Ultralong porous ZnO nanobelt arrays grown directly on fluorine-doped SnO2 substrate for dye-sensitized solar cells

Abstract

Arrays of novel ultralong nanoporous ZnO nanobelts (NBs) are developed with a two-step synthesis strategy. This strategy combines two processes, a rapid hydrothermal synthesis of vertically aligned ultralong Zn(OH)F NB arrays directly on fluorine-doped tin oxide (FTO) at pH = 8.5 and conversion of a pyrolysis Zn(OH)F NB intermediate into nanoporous ZnO NB. Two factors play crucial roles in the rapid synthesis of ultralong Zn(OH)F nanobelt (NB) arrays, i.e., the pretreatment of the FTO substrate before entering the aqueous solution of Zn2+ (2 M) and the presence of excess F− in the hydrothermal reaction solution. Upon the subsequent pyrolysis of the Zn(OH)F precursor at 500 °C for 2 h, ultralong nanoporous ZnO NB arrays are successfully generated. In addition, every NB is composed of a large number of nanocrystals and nanopores, which exhibit preferred orientation. Dye-sensitized solar cells (DSSCs) based on the ultralong porous ZnO NB arrays are assembled, and a high conversion efficiency (η) of 3.28% for a 27 μm thick film is obtained at 0.9 suns. This can be attributed to the high internal surface area and pronounced light scattering, as well as a good electron collection efficiency comparable with that of ZnO nanorod (NR)-based DSSCs.