Metal Electroplating of Three Dimensional (3D) Electrode in Electrolyte-less Dye Sensitized Solar Cells (ELDSC)
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Metal Electroplating of Three Dimensional (3D) Electrode in Electrolyte-less Dye Sensitized Solar Cells (ELDSC) Duen Yang Ong1,2, Meng Keong Lim2, Ziyu Jin1, Chee Lip Gan1, Kam Chew Leong2, and C. C. Wong1,* 1 School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue 639798, Singapore. 2 GLOBALFOUNDRIES Singapore Private Limited, 60 Woodlands Industrial Park D Street 2 738406, Singapore. * Corresponding author: Email: [email protected]; Tel: +65 67904595; Fax: +65 6790 9081
ABSTRACT The first Electrolyte-less dye sensitized solar cell (ELDSC) is proposed with the architecture of FTO-TiO2-dye-metal. In the ELDSC design, the most significant contact is the TiO2-dye-metal interface, whereby the metal electrode acts as the charge replenishment layer as well as the external electrode. In previous work, ELDSC has an inferior Fill Factor (FF) due to insufficient metal coverage from top-down physical vapor deposition. In this work, a three dimensional (3D) metal network plated through the mesoporous TiO2 network is achieved through bottom-up metal electroplating. This study focuses on the characteristics of electro deposition onto insulating planar TiO2 as well as mesoporous TiO2 network. For planar TiO2, gold (Au) islands form readily, becoming worm-like structures as they coalesce, subsequently becoming a continuous layer. (The plated metal on the insulating TiO2 layer is made possible by plane defects within the insulator layer that serve as the conductive supply path.) In contrast, electroplating carried out on a FTO-planar TiO2-mesoporous TiO2 substrate results in a 3D Au network within the mesoporous TiO2, where Au cords were observed as the connections among Au islands. This study demonstrates that a continuous metal layer can be electroplated onto an insulating TiO2 layer, borrowing its intrinsic planar defect network. Further, applying the same principle, a 3D metal network can be formed within mesoporous TiO2.
INTRODUCTION There are 6 main components in a typical Dye Sensitized Solar Cell (DSSC) [1]: conductive oxide substrate, photoanode, dye, electrolyte and counter electrode. The volatile solvents in the liquid electrolyte typically used in standard DSSC systems require robust encapsulation, prompting searches for substitutes such as ionic liquids [2-6]. Ionic liquids, on the other hand, are limited by inefficient penetration into the mesoporous titanium dioxide (TiO2) due to high viscosity. Thus the issue of the electrolyte in a DSSC still awaits an optimized solution. In 2011, the first Electrolyte-less dye sensitized solar cell (ELDSC) with the architecture of TiO2-dye-metal [7] was introduced to be the all-solid state organic solar cell. In previous work, the ELDSC device performed below the standard predicted from the energy band diagram
[7]. This was because the ELDSC device suffered from insufficient coverage of metal electrode in the mesoporous TiO2 structure resulting from top-down metal deposition [8]. Hence, the ELDSC device, where the metal electrode was depos
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