Nanopyramid Structures with Light Harvesting and Self- Cleaning Properties for Solar Cells

In this chapter, inverted and upright nanopyramid structures with light-harvesting properties and self-cleaning hydrophobic surfaces suitable for solar cells are presented. Periodic nanopyramid structures with 400–700 nm features were fabricated using interference lithography and combined dry and wet etching processes. The inverted nanopyramids (INP) were applied at the front side of the solar cells using UV nanoimprint lithography. These structures provided effective light-trapping properties and led to oblique angle light scattering and a significant reduction in reflectance resulting in higher power conversion efficiency. The second type, the periodic upright nanopyramid (UNP) structures were applied on a glass substrate by UV nanoimprint process. The glass cover is also utilized as a protective encapsulant front layer. The use of the upright nanopyramid structured cover glass in the encapsulated solar cell has also enhanced the power conversion efficiency due to the antireflection and strong light-scattering properties compared to the bare cover glass. In addition, the upright nanopyramid structured cover glass exhibited excellent self-cleaning of dust particles by rolling down water droplets. These results suggest that the nanopyramid structures with light-harvesting and self-cleaning properties can improve the performance of different types of solar cells, including thin films and glass-based PVs

Fabrication and Replication of Periodic Nanopyramid Structures by Laser Interference Lithography and UV Nanoimprint Lithography for Solar Cells Applications

In this chapter, the fabrication and replication of periodic nanopyramid structures suitable for antireflection and self-cleaning surfaces are presented. Laser interference lithography (LIL), dry etching, wet etching, and UV nanoimprint lithography (UV-NIL) are employed for the fabrication and replication of periodic nanopyramid structures. Inverted nanopyramid structures were fabricated on Si substrates by LIL and subsequent pattern transfer process using reactive ion etching, followed by potassium hydroxide (KOH) wet etching. The fabricated periodic inverted nanopyramid structures were utilized as a master mold for the nanoimprint process. The upright nanopyramid structures were patterned on the OrmoStamp-coated glass substrate with high fidelity in the first nanoimprint process. In the second nanoimprint process, inverted nanopyramid structures were replicated on the OrmoStamp-coated substrate using the fabricated upright nanopyramid glass substrate as a mold. The replicated inverted nanopyramid structure on resist-coated substrate was faithfully resolved with the high accuracy compared to original Si master mold down to nanometer scale. Both upright and inverted nanopyramid structures can be utilized as surface coatings for light trapping and self-cleaning applications for different types of solar cell and glass surfaces

Microdevice-based mechanical compression on living cells

Compressive stress enables the investigation of a range of cellular processes in which forces play an important role, such as cell growth, differentiation, migration, and invasion. Such solid stress can be introduced externally to study cell response and to mechanically induce changes in cell morphology and behavior by static or dynamic compression. Microfluidics is a useful tool for this, allowing one to mimic in vivo microenvironments in on-chip culture systems where force application can be controlled spatially and temporally. Here, we review the mechanical compression applications on cells with a broad focus on studies using microtechnologies and microdevices to apply cell compression, in comparison to off-chip bulk systems. Due to their unique features, microfluidic systems developed to apply compressive forces on single cells, in 2D and 3D culture models, and compression in cancer microenvironments are emphasized. Research efforts in this field can help the development of mechanoceuticals in the future

Finite-size and Disorder Effects on Unipartite and Bipartite Surface Lattice Resonances

Optical resonances in bipartite metal nanostructure lattices are more resilient to finite size-effects than equivalent unipartite lattices, but the complexities of their behaviour in non-ideal settings remain relatively unexplored. Here we investigate the quality factor and extinction efficiency of 1D Ag and Au unipartite and bipartite lattices. By modelling finite size lattices over a range of periods we show that the quality factor of Ag bipartite lattices is significantly better than unipartite lattices. This improvement is less pronounced for Au bipartite lattices. We also show that bipartite lattices are dramatically affected by structure size variations at scales that are typically seen in electron beam lithography fabrication in contrast to unipartite lattices, which are not as sensitive

Application of sequential cyclic compression on cancer cells in a flexible microdevice

Mechanical forces shape physiological structure and function within cell and tissue microenvironments, during which cells strive to restore their shape or develop an adaptive mechanism to maintain cell integrity depending on strength and type of the mechanical loading. While some cells are shown to experience permanent plastic deformation after a repetitive mechanical tensile loading and unloading, the impact of such repetitive compression on deformation of cells is yet to be understood. As such, the ability to apply cyclic compression is crucial for any experimental setup aimed at the study of mechanical compression taking place in cell and tissue microenvironments. Here, we demonstrate such cyclic compression using a microfluidic compression platform on live cell actin in SKOV-3 ovarian cancer cells. Live imaging of the actin cytoskeleton dynamics of the compressed cells was performed for varying pressures applied sequentially in ascending order during cell compression. Additionally, recovery of the compressed cells was investigated by capturing actin cytoskeleton and nuclei profiles of the cells at zero time and 24 h-recovery after compression in end point assays. This was performed for a range of mild pressures within the physiological range. Results showed that the phenotypical response of compressed cells during recovery after compression with 20.8 kPa differed observably from that for 15.6 kPa. This demonstrated the ability of the platform to aid in the capture of differences in cell behaviour as a result of being compressed at various pressures in physiologically relevant manner. Differences observed between compressed cells fixed at zero time or after 24 h-recovery suggest that SKOV-3 cells exhibit deformations at the time of the compression, a proposed mechanism cells use to prevent mechanical damage. Thus, biomechanical responses of SKOV-3 ovarian cancer cells to sequential cyclic compression and during recovery after compression could be revealed in a flexible microdevice. As demonstrated in this work, the observation of morphological, cytoskeletal and nuclear differences in compressed and non-compressed cells, with controlled micro-scale mechanical cell compression and recovery and using livecell imaging, fluorescent tagging and end point assays, can give insights into the mechanics of cancer cells

Generation of Micro-Droplets for the Study of Droplet Coalescence and Self-propulsion

Microfluidic devices play an ever increasing role in nano- and biotechnologies. An example of the recent breakthrough allowed by such technologies is the Lab-on-a- Chip (LOC), which enables orders of magnitude downsizing of assay equipment. An emerging area of research in this technology-driven field is digital microfluidics based upon the micromanipulation of discrete droplets. Microfluidic processing is performed on unit-sized packets of fluid which are transported, stored, mixed, reacted, or analysed in a discrete manner. Possible applications include on-chip assays, polymerase chain reaction, or DNA sequencing

Solid state AC electroosmosis micro pump on a chip

Lab-On-a-Chip (LOC) or Micro Total Analysis System (µTAS) technology requires precise control of minute amounts of liquid. Moving liquids in small capillaries requires bulky expensive external pumps that defy the purpose of microfabrication. By integrating a micropump into the device, it allows the system to be transportable, reliable, energy efficient and inexpensive. This system encompasses a solid-state AC electroosmotic pump for the manipulation of liquid containing cells or molecules. This paper reports extensively on the investigation of the pumping ability of the solid state array with KCl solution. Fluorescent beads of 500 nm where used as tracer to monitor the fluid velocity. Two different array geometries were investigated as well as different material for the electrodes. Dielectorphoretic trapping of nanoparticles and cells was achieved. This paper will discuss the inherent problem of an AC electroosmosis driven micropump for lab on chip applications as well as the fluid flow yield in both directions and magnitude in correlation with electric field intensity and frequency

High efficiency perovskite solar cells using DC sputtered compact TiO

High conductivity and transparency of the electron-transporting layer (ETL) is essential to achieve high efficiency perovskite solar cells (PvSCs). Generally, titanium dioxide (TiO2) has been extensively utilized as an ETL in PvSCs. Both surface roughness and uniformity of the compact-TiO2 (C-TiO2) can influence the efficiency of the PvSC. This work investigates the optimization of the direct current (DC) sputtering power and the ratio of argon (Ar) to oxygen (O2) plasma to achieve high quality ETL films. The effect of changing the DC sputtering power on the C-TiO2 films and subsequently on the overall efficiency was studied. The electrical and optical properties of the C-TiO2 layer were characterized for various DC powers and different ratios of Ar to O2 plasma. It was found that the optimum preparation conditions for the C-TiO2 films were obtained when the DC power was set at 200 W and a flow rate of 6 sccm Ar and 12 sccm O2. A power conversion efficiency (PCE) of 15.3% in forward sweep and 16.7% in reverse sweep were achieved under sunlight simulator of 100 mW/cm2. These results indicate that significant improvement in the efficiency can be achieved, by optimizing the C-TiO2 layer