Stergiopoulos T, Valota A, Likodimos V, Speliotis Th, Niarchos D, Skeldon P, Thompson G E, Falaras P
Institute of Physical Chemistry, NCSR Demokritos, GR-15310 Aghia Paraskevi Attikis, Athens, Greece.
Nanotechnology. 2009 Sep 9;20(36):365601. doi: 10.1088/0957-4484/20/36/365601. Epub 2009 Aug 18.
Self-organized porous TiO(2) nanotubes (NTs) were prepared on conductive glass by galvanostatic anodizing of sputtered titanium in an NH(4)F /glycerol electrolyte. DC magnetron sputtering at an elevated substrate temperature (500 degrees C) was used to deposit 650 nm thick titanium films. After anodizing, NTs, 830 nm long, with an average external diameter of 92 nm, were grown; this gave a high conversion rate of oxide from titanium (1.9), with a 220 nm thick layer of titanium, which was not oxidized, located at the base of the tubes. The NTs revealed a mainly amorphous structure, which transformed mostly to anatase upon thermal treatment in air at 450 degrees C. The tubes were sensitized by the N719 complex and the resultant photoelectrodes were incorporated into liquid dye solar cells (DSCs) and further tested under back-side illumination. High values of V(oc) (714 mV) were obtained under 1 sun (AM 1.5), assigned to low dark current magnitude and large recombination resistance and electron lifetime. In addition, typical values of fill factors (of the order of 0.62) were attained, in agreement with the estimated ohmic resistance of the cells in combination with low electron transfer resistance at the platinum/electrolyte interface. The overall moderate power conversion efficiency (of the order of 0.3%) was mainly due to the low short-circuit photocurrents (J(sc) = 0.68 mA cm(-2)), which was confirmed further by the corresponding IPCE values (5.2% at 510 nm). The magnitude of J(sc) was attributed to absorbed light losses due to back-side illumination of the cells, the low dye loading (due to the limited thickness of anodic titania) and the high charge transfer resistance at the TiO(2)/conductive substrate due to the presence of barrier layer(s) underneath the tubes. These preliminary results encourage the DSC community to explore further the galvanostatic anodizing of titanium in order to produce highly efficient porous TiO(2) NTs directly on conductive glass. Current work is focusing on achieving complete anodizing of the metal substrate and full transparency for the photoelectrode in order to increase and optimize the resultant cell efficiencies.
通过在NH₄F/甘油电解液中对溅射钛进行恒电流阳极氧化，在导电玻璃上制备了自组织多孔TiO₂纳米管（NTs）。在升高的衬底温度（500℃）下采用直流磁控溅射沉积650nm厚的钛膜。阳极氧化后，生长出长度为830nm、平均外径为92nm的NTs；这使得钛的氧化物转化率很高（1.9），在管的底部有一层220nm厚未被氧化的钛层。NTs呈现出主要为非晶态的结构，在450℃空气中热处理后大部分转变为锐钛矿型。用N719配合物对这些管进行敏化，将所得光电极组装到液体染料太阳能电池（DSCs）中，并在背面光照下进一步测试。在1个太阳（AM 1.5）光照下获得了较高的V(oc)值（714mV），这归因于低暗电流强度、大的复合电阻和电子寿命。此外，填充因子达到了典型值（约为0.62），这与根据电池的估计欧姆电阻以及铂/电解液界面处低的电子转移电阻相符。整体中等的功率转换效率（约为0.3%）主要是由于短路光电流较低（J(sc)=0.68mA cm⁻²），相应的IPCE值（510nm处为5.2%）进一步证实了这一点。J(sc)的大小归因于电池背面光照导致的吸收光损失、低染料负载量（由于阳极二氧化钛厚度有限）以及由于管下方存在阻挡层而在TiO₂/导电衬底处的高电荷转移电阻。这些初步结果鼓励DSC领域进一步探索钛的恒电流阳极氧化，以便直接在导电玻璃上制备高效的多孔TiO₂ NTs。目前的工作重点是实现金属衬底的完全阳极氧化以及光电极的完全透明，以提高和优化所得电池的效率。
