Evolution of the eukaryotic ARP2/3 activators of the WASP family: WASP, WAVE, WASH, and WHAMM, and the proposed new family members WAWH and WAML

<p>Abstract</p> <p>Background</p> <p>WASP family proteins stimulate the actin-nucleating activity of the ARP2/3 complex. They include members of the well-known WASP and WAVE/Scar proteins, and the recently identified WASH and WHAMM proteins. WASP family proteins contain family specific N-terminal domains followed by proline-rich regions and C-terminal VCA domains that harbour the ARP2/3-activating regions.</p> <p>Results</p> <p>To reveal the evolution of ARP2/3 activation by WASP family proteins we performed a "holistic" analysis by manually assembling and annotating all homologs in most of the eukaryotic genomes available. We have identified two new families: the WAML proteins (WASP and MIM like), which combine the membrane-deforming and actin bundling functions of the IMD domains with the ARP2/3-activating VCA regions, and the WAWH protein (WASP without WH1 domain) that have been identified in amoebae, Apusozoa, and the anole lizard. Surprisingly, with one exception we did not identify any alternative splice forms for WASP family proteins, which is in strong contrast to other actin-binding proteins like Ena/VASP, MIM, or NHS proteins that share domains with WASP proteins.</p> <p>Conclusions</p> <p>Our analysis showed that the last common ancestor of the eukaryotes must have contained a homolog of WASP, WAVE, and WASH. Specific families have subsequently been lost in many taxa like the WASPs in plants, algae, Stramenopiles, and Euglenozoa, and the WASH proteins in fungi. The WHAMM proteins are metazoa specific and have most probably been invented by the Eumetazoa. The diversity of WASP family proteins has strongly been increased by many species- and taxon-specific gene duplications and multimerisations. All data is freely accessible via <url>http://www.cymobase.org</url>.</p

Comparison of mechanical and ultrasonic agitation methods for mono c-Si texturing

Texturing of a mono crystalline Si wafer aims to create light trapping structures to reduce the reflection losses. Being a cheap and efficient process, alkaline texturing of Si wafers is commonly used in all industrial mono crystalline solar cell production lines. However, standard process with potassium hydroxide ( KOH)-based solutions with isopropyl alcohol ( IPA) addition suffers from instability, high material consumption, and nonuniformities in the shape and the distribution of the pyramid structures formed on the Si surface. In this work, we studied the effect of ultrasonic agitation ( UA) during the etching process on the structural, optical, and electrical properties of mono crystalline Si solar cell as a function of process parameters. We have shown that UA improves optical and electrical performance of the cells by forming uniform pyramid structures. In addition, it also helps to lower the material consumption and Si removal from the surface by enabling less process time and temperature. Ultrasonic agitation of the etching solution proves to be a good modification of the wet process steps for the mono crystalline silicon solar cell technology. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Comparison of influence of gold contamination on the performances of planar and three dimensional c-Si solar cells

Radial junction solar cell is proposed as an alternative device geometry to planar junction solar cell due to its superior electro-optical performance. In this geometry, densely-packed micropillars enable the collection of minority carriers in the radial direction. Thus, the distance that carriers should travel to reach the p-n junction is shortened, allowing the use of low quality materials with poor carrier lifetime. In this study, we have experimentally studied the advantage of radial junction approach in low quality Si. For this purpose, we fabricated planar and radial junction solar cells using Si wafers with Au impurities. Average efficiency values of 15.74% and 15.66% were obtained for planar and radial cells in uncontaminated samples, respectively, indicating that close efficiency values were obtained when using high quality materials. However, in the case of contamination, the efficiency of the cells with radial junction degraded less compared to the planar junction with the values of 14.71% and 12.72%, respectively. This is consistent with the expectation that radial junction cells are less sensitive to the quality of the material used. Moreover, these results, together with future structural optimization, lay a solid foundation for lowering fabrication costs without reducing the performance of the solar cell

Effects of different laser modified surface morphologies and post-texturing cleanings on c-Si solar cell performance

Performance of crystalline Silicon solar cells depends on numerous factors. One key factor is a surface structure which can restrict electrical and optical properties due to recombination of generated carriers and reflection of incident light. Surface texturing reduces reflection from a flat surface which increases absorption of light. Anisotropic alkaline etchants are commonly used for texturing mono-crystalline Silicon wafers which produce pyramid structures on the surface. Because of randomly oriented crystallographic grains, this method is not feasible for multi-crystalline Silicon wafers. Here, an alternative texturing process using a laser system is proposed. Laser beam creates vertical and horizontal grooves on the surface in which the intersections are for a light trapping purpose. Laser parameters are determined experimentally to have the lowest reflection. Next, chemical post-texture cleaning is performed to remove laser-induced damages and other residues. Finally, samples went through general solar cell fabrication steps. For characterizations, weighted reflection is measured and correlated with Scanning Electron Microscopy images of a textured surface to evaluate the performance of texturing and post-texture cleaning. To examine fabricated solar cells' performance, I-V curve and External Quantum Efficiency are measured. Results indicate that proposed processes lead to an improved efficiency compared to reference samples

Radial junction solar cells prepared on single crystalline silicon wafers by metal-assisted etching

Radial junction solar cells have been proposed as an alternative device geometry to conventional planar solar cells with its remarkable electrical and optical performance. In this geometry, densely packed nano/micropillars allow minority carrier collection in the radial direction and shorten carrier diffusion length to p-n junction. Besides, reduced reflection from surface and increased light trapping in nano/micropillars enhance solar cell efficiency. In this study, photolithography and metal-assisted etching (MAE) techniques are used to form well-ordered silicon micropillar arrays; standard doping, passivation, and metallization steps are followed to form radial junction solar cells. The effect of micropillar length on optical and electrical performance of the solar cells have been investigated. We observed that optical reflection from solar cells surface decreased with increasing micropillar length, hence solar cell short circuit current (J(sc)) and efficiency (eta) increased. Our best solar cell efficiency is 15.6% and this is one of the highest reported values obtained from the radial junction solar cells prepared by MAE technique. (C) 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei