%0 Journal Article
%T ZnO-Nanorod Dye-Sensitized Solar Cells: New Structure without a Transparent Conducting Oxide Layer
%A Ming-Hong Lai
%A Auttasit Tubtimtae
%A Ming-Way Lee
%A Gou-Jen Wang
%J International Journal of Photoenergy
%D 2010
%I Hindawi Publishing Corporation
%R 10.1155/2010/497095
%X Conventional nanorod-based dye-sensitized solar cells (DSSCs) are fabricated by growing nanorods on top of a transparent conducting oxide (TCO, typically fluorine-doped tin oxideĦŞFTO). The heterogeneous interface between the nanorod and TCO forms a source for carrier scattering. This work reports on a new DSSC architecture without a TCO layer. The TCO-less structure consists of ZnO nanorods grown on top of a ZnO film. The ZnO film replaced FTO as the TCO layer and the ZnO nanorods served as the photoanode. The ZnO nanorod/film structure was grown by two methods: (1) one-step chemical vapor deposition (CVD) (2) two-step chemical bath deposition (CBD). The thicknesses of the nanorods/film grown by CVD is more uniform than that by CBD. We demonstrate that the TCO-less DSSC structure can operate properly as solar cells. The new DSSCs yield the best short-current density of 3.96£żmA/ and a power conversion efficiency of 0.73% under 85£żmW/ of simulated solar illumination. The open-circuit voltage of 0.80£żV is markedly higher than that from conventional ZnO DSSCs. 1. Introduction Dye-sensitized solar cells (DSSC) are a promising low-cost, green energy source [1, 2]. A power conversion efficiency of 11.18% has been achieved in 2005 [3]. The high efficiency of DSSCs can be attributed to the structure of a photoelectrode which consists of a layer of nanoparticle TiO2 sintered to a transparent-conducting oxide (TCO). The mesoporous TiO2 nanoparticles increase the surface area for dye chemisorptions to a thousand folds over that of a flat electrode of the same size [4]. The progress in enhancing the performance of DSSCs has been slow over the last decade. One of the main problems is the limited diffusion length of the photogenerated electrons. The photogenerated carriers conduct via random hopping through a percolated path in a three-dimensional network of nanoparticles. Previous studies have shown that the photogenerated carriers must undergo 103¨C106 hoppings (trapping and detrapping) before they reach the collecting electrodes [5]. Carrier trapping, presumably by defect states at the surface of nanoparticles [6, 7], leads to a low electron diffusion coefficient ( ) [8], which is several orders of magnitude smaller than that of single-crystal [9]. To improve the electron transport, researchers have tried to design DSSCs without a nanoparticulate structure. One promising approach is to replace the nanoparticles with crystalline TiO2 nanorods (or nanowires, nanotubes), thereby eliminating the grain boundaries between nanoparticles. TiO2-nanorod DSSCs have yielded
%U http://www.hindawi.com/journals/ijp/2010/497095/