National Nanotechnology Laboratory (NNL), Istituto Nanoscienze CNR, c/o Distretto Tecnologico, via per Arnesano km 5, 73100 Lecce, Italy.
J Am Chem Soc. 2011 Nov 30;133(47):19216-39. doi: 10.1021/ja208418z. Epub 2011 Nov 8.
A colloidal crystal-splitting growth regime has been accessed, in which TiO(2) nanocrystals, selectively trapped in the metastable anatase phase, can evolve to anisotropic shapes with tunable hyperbranched topologies over a broad size interval. The synthetic strategy relies on a nonaqueous sol-gel route involving programmed activation of aminolysis and pyrolysis of titanium carboxylate complexes in hot surfactant media via a simple multi-injection reactant delivery technique. Detailed investigations indicate that the branched objects initially formed upon the aminolysis reaction possess a strained monocrystalline skeleton, while their corresponding larger derivatives grown in the subsequent pyrolysis stage accommodate additional arms crystallographically decoupled from the lattice underneath. The complex evolution of the nanoarchitectures is rationalized within the frame of complementary mechanistic arguments. Thermodynamic pathways, determined by the shape-directing effect of the anatase structure and free-energy changes accompanying branching and anisotropic development, are considered to interplay with kinetic processes, related to diffusion-limited, spatially inhomogeneous monomer fluxes, lattice symmetry breaking at transient Ti(5)O(5) domains, and surfactant-induced stabilization. Finally, as a proof of functionality, the fabrication of dye-sensitized solar cells based on thin-film photoelectrodes that incorporate networked branched nanocrystals with intact crystal structure and geometric features is demonstrated. An energy conversion efficiency of 6.2% has been achieved with standard device configuration, which significantly overcomes the best performance ever approached with previously documented prototypes of split TiO(2) nanostructures. Analysis of the relevant photovoltaic parameters reveals that the utilized branched building blocks indeed offer light-harvesting and charge-collecting properties that can overwhelm detrimental electron losses due to recombination and trapping events.
已进入胶态晶体分裂生长阶段，在此阶段中，TiO(2)纳米晶体选择性地被困在亚稳的锐钛矿相中，可以在较宽的尺寸范围内演化成具有可调超支化拓扑结构的各向异性形状。该合成策略依赖于非水溶胶-凝胶途径，涉及通过简单的多注入反应物输送技术在热表面活性剂介质中程序化激活钛羧酸酯配合物的氨解和热解。详细的研究表明，在氨解反应中最初形成的支化物体具有应变单晶骨架，而在随后的热解阶段中生长的较大衍生物则在晶格下从晶格中晶向分离的位置容纳了额外的支链。纳米结构的复杂演化是在互补的机制论点框架内合理化的。热力学途径由锐钛矿结构的形状导向效应和分支以及各向异性发展伴随的自由能变化决定，被认为与动力学过程相互作用，这些动力学过程与扩散限制、空间不均匀单体通量、瞬态 Ti(5)O(5) 畴中的晶格对称破缺以及表面活性剂诱导的稳定化有关。最后，作为功能的证明，基于包含具有完整晶体结构和几何特征的网络支化纳米晶体的薄膜光电管制造染料敏化太阳能电池得到了证明。采用标准器件配置实现了 6.2%的能量转换效率，这明显超过了具有以前记录的分裂 TiO(2)纳米结构原型的最佳性能。相关光伏参数的分析表明，所使用的支化构建块确实提供了光捕获和电荷收集特性，可以克服由于复合和俘获事件引起的有害电子损失。
