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Introduction of diamond-wire-sawing (DWS) technique has resulted in significant cost reduction for silicon (Si) wafering process. Unlike slurry-wire-sawn (SWS) wafers, DWS wafer has fewer, non-uniform and thinner saw damage surface. Acid texturing on such surfaces yield highly reflecting and non-uniform texture formation. An additive-free, low cost, non-metallic, energy efficient acid based texturing scheme, named as NCPRE acid texturing, is demonstrated here for DWS multicrystalline Si wafers. The NCPRE acid texturing process employs specific Hydrofluoric-Nitric acid solution to obtain uniform porous silicon (Por-Si) layer. A total of 672 and 1204 cells were fabricated employing the NCPRE acid texturing and additive based acid texturing processes respectively using inline industrial diffusion tools. An impressive batch efficiency of 18.25% is obtained for the NCPRE textured cells against 18.31% cost intensive additive based textured cells. Reasonably close values of cell efficiency establish NCPRE acid texturing a potential candidate for efficient and low-cost DWS mc-Si wafer texturing process.

Power loss due to dust deposition on photovoltaic (PV) modules (also referred to as soiling) is a severe challenge to the economic viability of PV deployment in sunbelt countries like India and the Middle East. Anti-soiling coatings are nano/micrometer thick transparent coatings, which mitigate dust deposition on PV module. In this study, Tapping Mode Atomic Force Microscopy (TM-AFM) phase imaging was used to characterize the surface changes of four different commercial hydrophobic anti-soiling coatings as they were subjected to outdoor field exposure tests and three different indoor accelerated stress tests. The anti-soiling coatings were applied via manual spray coating method on solar glass substrates. The phase angle for not-coated glass shows a tight distribution around zero. The phase angle distribution of coated surface showed a larger spread. When the coatings were subjected to different environmental stressors, the phase angle distributions became tighter and, in some cases, collapsed to tight distributions around zero, indicating that the coatings were partly or completely removed from the glass surface. We demonstrate a correlation of the changes in surface coverage identified from phase angle distributions to contact angle and surface roughness, thus establishing TM-AFM phase imaging as a promising approach to characterize anti-soiling coatings subjected to environmental stress. While the analysis of the phase angle distribution is able to resolve the removal of the coating, contact angle and surface roughness cannot do so unambiguously.

Graphene with varying number of layers is explored as metal gate electrode in metal oxide semiconductor structure by inserting it between the dielectric (SiO2) and contact metal (TiN) and results are compared with TiN gate electrode. We demonstrate an effective work function tuning of gate electrode upto 0.5 eV by varying the number of graphene layers. Inclusion of even 1-3 layers of graphene results in significantly improved dielectric reliability as measured by breakdown characteristics, charge to breakdown, and interface state density. These improvements are attributed to the impermeability of graphene for TiN and hence reduced metallic contamination in the dielectric. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726284]