In dye-sensitized solar cells based on anodic titania nanotube arrays, the low photocurrent in the backside-illuminated configuration has hindered their development. To increase the energy absorption and thus promote the photocurrent, a novel parallel configuration of dye-sensitized solar cells is proposed and achieved in this work on the basis of double-sided anodic nanotubes. The parallel connection is verified by electrochemical impedance spectroscopy measurements. The parallel cells exhibit an average 70% increment in photocurrent and 30% enhancement in efficiency as compared to the single cells, due to significantly increased surface area and highly reduced series resistance. Theoretical calculation and experimental fitting results demonstrate that a tube length of $30 mm is optimal for the nanotubes used in this study with backside-illuminated architecture.

Anodic formation of titania nanowires has been interpreted using a bamboo-splitting model; however, a number of phenomena are difficult to explain with this model. Herein, transition from nanotubes to nanowires is investigated by varying the anodizing conditions. The results indicate that the transition requires a large number of hydrogen ions to reduce the passivated area of tube walls, and therefore can be observed only in an intermediate chemical dissolution environment. Accordingly, a model in terms of stretching and splitting is proposed to interpret the transition process. The model provides a basis to suppress the nanowires with surface treatments before anodization and to clear the nanowires with an ultrasonication process after anodization. The nanotube-nanowire transition also arises when the tubes are directly used in dye-sensitized solar cells. Treatment with titanium tetrachloride solution for about 10 h is found to be effective in suppressing the nanowires, and thus improving the photovoltaic properties of the solar cells.

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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 .