Abstract

ZnO thin films are prepared on the glass, GaAs (100), Si(111), and Si(100) substrates at different temperatures by the pulsed laser deposition (PLD) method. X-ray diffraction (XRD) measurements indicate that the substrate temperatures of 200–500, 200–500, 300–500, and 300–500 °C are the optimized conditions of crystalline for the glass, GaAs (100), Si (111), and Si (100) substrates, respectively. In spite of the films deposited on the different substrates, the films always show (002) orientation at the optimized conditions. Photoluminescence (PL) results indicate that the thin films fabricated at the optimized conditions show the intense near band PL emissions. The optimized conditions for PL are 500, 500, 400–500, and 500 °C for glass, GaAs (100), Si (111), and Si (100) substrates, respectively.

TiO2/ZnO and N-doped TiO2/ZnO composite nanotube arrays were synthesized by the sol-gel method using ZnOnanorod arrays as a template. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance UV-Vis spectroscopy (UV-Vis) were used to characterize the samples. The nanotubes had a uniform hexagonal shape. The diameter and wall thickness of the nanotubes were about 100 nm and 20 nm, respectively. Some N dopants were substitutionally doped into the TiO2 lattice, while the N-Ox, N-C, and N-N were chemically absorbed onto the surface of the TiO2/ZnO composite nanotubes. Dopant-induced narrowing of the bandgap resulted from the doping of N ions into the TiO2 lattices. The surface N species enhanced the visible-light response and promoted the separation of photogenerated carriers. Compared with the TiO2/ZnO composite nanotube arrays, the N-TiO2/ZnO composite nanotube arrays exhibited higher photocatalytic activity.

以ZnO纳米柱阵列为模板, 采用溶胶-凝胶法制备出TiO2/ZnO和N掺杂TiO2/ZnO的复合纳米管阵列. 扫描电镜(SEM)、X射线光电子能谱(XPS)和紫外-可见漫反射吸收光谱(UV-Vis)的结果表明: 两种阵列的纳米管均为六角形结构, 直径约为100 nm, 壁厚约为20 nm; 在N-TiO2/ZnO复合纳米管阵列中, 掺入的N离子主要是以N-Ox、N-C和N-N的形式化学吸附在纳米管表面, 仅有少量的N离子以取代式掺杂的方式占据TiO2晶格O的位置; 表面N物种形成的表面态能级和取代式掺杂导致带隙的窄化, 增强了纳米管阵列的光吸收效率, 促进了光生载流子的分离. 光催化实验结果表明, N离子的掺杂有利于N-TiO2/ZnO复合纳米管阵列光催化活性的提高.

Abstract

Dye-sensitized solar cells (DSSCs) are fabricated based on hollow anatase TiO₂ (HA-TiO₂) spheres synthesized by a chemically induced self-transformation (CIST) strategy using urea as a base catalyst, whose walls are composed of anatase nanocrystals and exhibit hierarchical porosity. TiO₂ hollow structured materials not only have low density, high specific surface areas, and hierarchically porous structures, but also exhibit high light-collection efficiency and fast motion of charge carriers. Effects of calcination temperatures on the performance of HA-TiO₂ solar cells are investigated and discussed. With increasing calcination temperatures, the light–electricity conversion efficiencies (η) increase. At 600 °C, HA-TiO₂ cells reach the highest efficiency. The performances of HA-TiO₂ cells are also compared with Degussa P-25 (P25) TiO₂ nanoparticle cells at the same film thickness, and their optimal efficiencies at 600 °C are 4.82 and 4.35%, respectively. The enhanced performance of HA-TiO₂ cells is due to their high surface area and hierarchically nanoporous structures when compared with the nonporous TiO₂ nanoparticles (P25).

Abstract

In the present work, we produce 15 μm thick titania mesosponge layers (TMSL) by a Ti anodization/etching process and use the layers in dye-sensitized solar cells (DSCs). We show that the solar cell efficiency can considerably be improved by a TiCl₄ hydrolysis treatment (increase of approx. 40% to an overall value of 4.9% under AM 1.5 illumination). This beneficial effect is due to the decoration of the ∼10 nm wide channels present in TMSL with TiO₂ nanoparticles of approx. 3 nm diameter, which allow for a significantly higher specific dye loading of the TMS structure.