Counter electrodes, as one of important components in dye-sensitized solar cells (DSSCs), play a role of transferring electrons arriving from external circuit back to the iodide (I^-)/triiodide (I₃^-) redox electrolyte and to catalyze the reduction of the redox couple [1]. Although sputtered-platinum (SP-Pt) on conducting glass, such as ITO or FTO, was generally used as the counter electrode in DSSCs for I₃^- reduction, less attention has been paid to increase the active surface area for I₃⁻ reduction as well as the cell efficiency by controlling the morphology of Pt through adding the surfactant in the electrodeposition bath.   .          

In this study, a Pt counter electrode for ZnO-based DSSCs was prepared by electrochemical deposition of H₂PtCl₆ on ITO substrate in the presence of nonionic surfactant, t-octylphenoxypolyethoxyethanol (Triton^® X-100). Triton^® X-100 was selected to achieve an ordered structure for the electrochemically deposited Pt, which is based on the fact that a nonionic surfactant forms liquid crystalline phase that can be used as a template for the production of a well-defined mesoporous Pt [2]. Cyclic voltammetry (CV) was utilized here to compare the I⁻/I₃⁻ redox behavior between the SP-Pt electrode and the electrodeposited-Pt (ED-Pt) electrode. Both the peak current density and the charge capacity for the ED-Pt film are larger than those of the SP-Pt film. This can be interpreted in terms of increased active surface area of this film. The ZnO-based cells fabricated with an ED-Pt counter electrode showed a higher conversion efficiency of 1.69% compared with cell fabricated with a SP-Pt (1.21%) counter electrode under the illumination of 100 mW/cm². The enhancement was attributed to the increase in the effective surface area of Pt for I₃⁻ reduction.

References:

[1] N. Papageorgiou, W.F. Maier, M. Grätzel, J. Electrochem. Soc. 114 (1997) 876.

[2] G. S. Attard, P. N. Bartlett, N. R. B. Coleman, J. M. Elliott, J. R. Owen, J. H. Wang, Science 278 (1997) 838.

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