In the present work, we show that fully functional self-organized TiO(2) nanotube layers can be electrochemically grown with an unprecedented growth rate if lactic acid (LA) is used as an additive during anodization. The main effect of LA addition is that it allows performing nanotube growth at significantly higher anodization voltage than in the LA free case, and this without dielectric oxide breakdown ("burning"). As a result, for example, 15 μm tube thick nanotube layers, suitable for a use in dye-sensitized solar cells (DSSCs) can be grown in 45 s and 7 μm tubes suitable for water splitting can be grown in 25 s.

A new series of stable, unsymmetrical squaraine near-IR sensitizers (JK-216 and JK-217), which are assembled using both thiophenyl pyrrolyl and indolium groups, exhibit a panchromatic light harvesting up to 780 nm. The JK-216 based cell exhibited a record efficiency of 6.29% for near-IR DSSCs. In addition, the JK-217 device showed an excellent stability under a light soaking test at 60 °C for 1000 h.

This document is the Accepted Manuscript version of the following published work:Hierarchical DSSC structures based on "single walled" TiO2 nanotube arrays reach a back-side illumination solar light conversion efficiency of 8%, Seulgi So, Imgon Hwang and Patrik Schmuki, Energy Environ. Sci., 2015,8, 849-854. To access the final edited and published work see:http://pubs.rsc.org/en/Content/ArticleLanding/2015/EE/c4ee03729d#!divAbstract DOI: 10.1039/C4EE03729D 1 AbstractIn the present work we introduce a path to the controlled construction of DSSCs based on hierarchically structured single walled, self-organized TiO 2 layers. In a first step we describe a simple approach to selectively remove the inner detrimental shell of anodic TiO 2 nanotubes (NTs). This then allows controlled well-defined layer-by-layer decoration of these TiO 2 -NT walls with TiO 2 nanoparticles (this in contrast to conventional TiO 2 nanotubes). We show that such defined multiple layered decoration can be optimized to build dye sensitized solar cells that (under back-side illumination conditions) can yield solar light conversion efficiencies in the range of 8 %. The beneficial effects observed can be ascribed to a combination of three factors : 1) improved electronic properties of the "single walled" tubes themselves, 2) a further improvement of the electronic properties by the defined TiCl 4 treatment, and 3) a higher specific dye loading that becomes possible for the layer-by-layer decorated single walled tubes.

A B S T R A C TOver the past ten years, self-aligned TiO 2 nanotubes have attracted tremendous scientific and technological interest due to their anticipated impact on energy conversion, environment remediation and biocompatibility. In the present manuscript, we review fundamental principles that govern the self-organized initiation of anodic TiO 2 nanotubes. We start with the fundamental question: Why is self-organization taking place? We illustrate the inherent key mechanistic aspects that lead to tube growth in various different morphologies, such as rippled-walled tubes, smooth tubes, stacks and bamboo-type tubes, and importantly the formation of double-walled TiO 2 nanotubes versus single-walled tubes, and the drastic difference in their physical and chemical properties. We show how both double-and single-walled tube layers can be detached from the metallic substrate and exploited for the preparation of robust self-standing membranes.Finally, we show how by selecting the "right" growth approach to TiO 2 nanotubes specific functional features can be significantly improved, e.g., an enhanced electron mobility, intrinsic doping, or crystallization into pure anatase at extremely high temperatures can be achieved. This in turn can be exploited in constructing high performance devices based on anodic TiO 2 in a wide range of applications.