Dye-sensitized solar cells based on ZnO nanotetrapods

Abstract

In this paper, we reviewed recent systematic studies of using ZnO nanotetrapods for photoanodes of dye-sensitized solar cells (DSSCs) in our group. First, the efficiency of power conversion was obtained by more than 3.27% by changes of conditions of dye loading and film thickness of ZnO nanotetrapod. Short-circuit photocurrent densities (J sc ) increased with the film thickness, J sc would not be saturation even the film thickness was greater than 35 μm. The photoanode architecture had been charactered by good crystallinity, network forming ability, and limited electron-hopping interjunctions. Next, DSSCs with high efficiency was devised by infiltrating SnO 2 nanoparticles into the ZnO nanotetrapods photoanodes. Due to material advantages of both constituents described as above, the composite photoanodes exhibited extremely large roughness factors (RFs), good charge collection, and tunable light scattering properties. By varying the composition of the composite photoanodes, we had achieved an efficiency of 6.31% by striking a balance between high efficiency of charge collection for SnO 2 nanoparticles rich films and high light scattering ability for ZnO nanotetrapods rich films. An ultrathin layer of ZnO was found to form spontaneously on the SnO 2 nanoparticles, which primarily was responsible for enhancing open-circuit photovoltage (V oc ). We also identified that recombination in SnO 2 /ZnO composite films was mainly determined by ZnO shell condition on SnO 2 , whereas electron transport was greatly influenced by the morphologies and sizes of ZnO crystalline additives. Finally, we applied the composite photoanodes of SnO 2 nanoparticles/ZnO nanotetrapods to flexible DSSCs by low temperature technique of "acetic acid gelation-mechanical press-ammonia activation." The efficiency has been achieved by 4.91% on ITO-coated polyethylenenaphtalate substrate. The formation of a thin ZnO shell on SnO 2 nanoparticles, after ammonia activation, was also found to be critical to boosting V oc and to improving inter-particles contacts. Mechanical press, apart from enhancing film durability, also significantly improved charge collection. ZnO nanotetrapods had been demonstrated to be a better additive than ZnO particles for the improvement of charge collection in SnO 2 /ZnO composite photoanodes regardless of whether they were calcined.

Recent advances in solar cells based on one-dimensional nanostructure arrays

“…It should be noted that besides the widely reported arrays of 1D nanowires, nanopillars, nanorods, nanotubes, and nanofibers, recent studies have demonstrated that solar cells based on nanohole arrays (Fig. 19a-b), [104][105][106][107] zigzag structure arrays, 108 branched nanowire arrays or nanoforests, 77,78 nanocrystallite aggregates, 81,83 nanograting arrays, 109 nanospike arrays, 110 and nanocomposites of 0D and 1D materials, 68,69,75,[85][86][87]98 etc. also show superior light trapping capability and thus, higher power conversion efficiency.…”

“…As shown in Fig. 14, a variety of 3D nanostructures such as ZnO nanotetrapods, 74,75 branched ZnO nanowires, 76 ZnO or TiO 2 nanoforests, 77,78 dendritic ZnO nanowires, 79 ZnO nanoflowers, 80 ZnO aggregates, 81 TiO 2 nanotubes on titanium mesh, 82 nanoporous TiO 2 spheres, 83 and hollow TiO 2 hemispheres 84 have been reported. It was found that these 3D nanostructure photoelectrodes can indeed improve photovoltaic performance.…”

“…Particularly, DSSCs based on ZnO or TiO 2 nanoparticle aggregates exhibited very high conversion efficiency of 5.4% 81 and 10.5%, 83 respectively, possibly due to very the high surface area, strong light scattering and short diffusion distance. 81,83 Furthermore, recent investigations demonstrated that hybrid structures of ZnO nanotetrapods/SnO 2 nanoparticles, 75,85 hierarchical ZnO 86 or TiO 2 nanodendrites/nanoparticles 87 may be promising photoelectrodes for high-efficiency DSSCs. 5 Solar cells based on electrospun nanofibers 5.1 Electrospun nanofibers as DSSC photoelectrodes 5.1.1 TiO 2 and ZnO nanofibers.…”

Novel photoanode based on hierarchically structured Ti–P double oxide

“…Therefore, one of the solutions to these problems is to obtain microstructured systems assembled from nanotubes, nanoplates and etc. [4,5,[12][13][14][15]. Such an approach will provide the material with a developed surface, a large particle size that is comparable to the wavelength of visible light, can increase the efficiency of light collection due to the effective scattering effect.…”

Influence of defect density on the ZnO nanostructures of dye-sensitized solar cells

“…Owning to the easy crystallization and anisotropic growth, various ZnO nanostructures such as nanoparticles [1][2][3], nanorods [4][5][6][7][8], nanotubes [9][10][11][12], nanoflowers [13], nanosheets [14], tetrapods [15], nanotrees [16], nanowire-nanosheet [17], nanoforest [18], nanodendrite/nanoparticle composite [19] and multilayer nanowires [20] have been reported in DSSCs. Researchers generally focused on the design of various nanostructured semiconducting materials with emphasis on optimizing dye loading, and less on ZnO material properties themselves such as defect concentration.…”