Metal electroplating of three dimensional (3D) electrode in Electrolyte-less Dye Sensitized Solar Cells (ELDSC)

The first Electrolyte-less dye sensitized solar cell (ELDSC) is proposed with the architecture of FTO-TiO ₂-dye-metal. In the ELDSC design, the most significant contact is the TiO ₂-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 TiO ₂ network is achieved through bottom-up metal electroplating. This study focuses on the characteristics of electro deposition onto insulating planar TiO ₂ as well as mesoporous TiO ₂ network. For planar TiO ₂, gold (Au) islands form readily, becoming worm-like structures as they coalesce, subsequently becoming a continuous layer. (The plated metal on the insulating TiO ₂ 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 TiO ₂-mesoporous TiO ₂ substrate results in a 3D Au network within the mesoporous TiO ₂, 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 TiO ₂ layer, borrowing its intrinsic planar defect network. Further, applying the same principle, a 3D metal network can be formed within mesoporous TiO ₂.