Challenges and prospects of nanopillar-based solar cells

Materials and device architecture innovations are essential for further enhancing the performance of solar cells while potentially enabling their large-scale integration as a viable source of alternative energy. In this regard, tremendous research has been devoted in recent years with continuous progress in the field. In this article, we review the recent advancements in nanopillar-based photovoltaics while discussing the future challenges and prospects. Nanopillar arrays provide unique advantages over thin films in the areas of optical properties and carrier collection, arising from their three-dimensional geometry. The choice of the material system, however, is essential in order to gain the advantage of the large surface/interface area associated with nanopillars with the constraints different from those of the thin film devices. © Tsinghua University Press and Springer-Verlag 2009

Shape-Controlled Synthesis of Single-Crystalline Nanopillar Arrays by Template-Assisted Vapor-Liquid-Solid Process

Highly regular, single-crystalline nanopillar arrays with tunable shapes and geometry are synthesized by the template-assisted vapor-liquid-solid growth mechanism. In this approach, the grown nanopillars faithfully reproduce the shape of the pores because during the growth the liquid catalyst seeds fill the space available, thereby conforming to the pore geometry. The process is highly generic for various material systems, and as an example, CdS and Ge nanopillar arrays with square, rectangular, and circular cross sections are demonstrated. In the future, this technique can be used to engineer the intrinsic properties of NPLs as a function of three independently controlled dimensional parameters - length, width and height. © 2010 American Chemical Society

Ordered Arrays of Dual-diameter Nanopillars for Maximized Broadband Optical Absorption

Optical properties of highly ordered Ge nanopillar arrays are tuned through shape and geometry control to achieve the optimal absorption efficiency. Increasing the Ge materials filling ratio is shown to increase the reflectance while simultaneously decreasing the transmittance, with the absorbance showing a strong diameter dependency. To enhance the broad band optical absorption efficiency, a novel dual-diameter nanopillar structure is presented, with a small diameter tip for minimal reflectance and a large diameter base for maximal effective absorption coefficient. The enabled single-crystalline absorber material with a thickness of only 2 μm exhibits an impressive absorbance of ∼99% over wavelengths, λ = 300-900 nm. These results enable a viable and convenient route toward shape-controlled nanopillar-based high-performance photonic devices. © 2010 American Chemical Society

Thigh-length compression stockings and DVT after stroke

Controversy exists as to whether neoadjuvant chemotherapy improves survival in patients with invasive bladder cancer, despite randomised controlled trials of more than 3000 patients. We undertook a systematic review and meta-analysis to assess the effect of such treatment on survival in patients with this disease