Laser applications in thin-film photovoltaics

We review laser applications in thin-film photovoltaics (thin-film Si, CdTe, and Cu(In,Ga)Se2 solar cells). Lasers are applied in this growing field to manufacture modules, to monitor Si deposition processes, and to characterize opto-electrical properties of thin films. Unlike traditional panels based on crystalline silicon wafers, the individual cells of a thin-film photovoltaic module can be serially interconnected by laser scribing during fabrication. Laser scribing applications are described in detail, while other laser-based fabrication processes, such as laser-induced crystallization and pulsed laser deposition, are briefly reviewed. Lasers are also integrated into various diagnostic tools to analyze the composition of chemical vapors during deposition of Si thin films. Silane (SiH4), silane radicals (SiH3, SiH2, SiH, Si), and Si nanoparticles have all been monitored inside chemical vapor deposition systems. Finally, we review various thin-film characterization methods, in which lasers are implemente

Existence of positive solutions of a superlinear boundary value problem with indefinite weight

We deal with the existence of positive solutions for a two-point boundary value problem associated with the nonlinear second order equation $u''+a(x)g(u)=0$. The weight $a(x)$ is allowed to change its sign. We assume that the function $g\colon\mathopen{[}0,+\infty\mathclose{[}\to\mathbb{R}$ is continuous, $g(0)=0$ and satisfies suitable growth conditions, so as the case $g(s)=s^{p}$, with $p>1$, is covered. In particular we suppose that $g(s)/s$ is large near infinity, but we do not require that $g(s)$ is non-negative in a neighborhood of zero. Using a topological approach based on the Leray-Schauder degree we obtain a result of existence of at least a positive solution that improves previous existence theorems.Comment: 12 pages, 4 PNG figure

Study on the suitable lighting design of Beato Angelico’s artworks displayed at the National Museum of San Matteo in Pisa (Italy)

The lighting design of exhibition space has a great impact on visual and colour perception and different lighting arrangements can create very different visual impression of artworks and, if not carefully designed, compromise the enjoyment of the viewers. This study involved the design of a new lighting solution for two of Beato Angelico’s artworks displayed at the National Museum of San Matteo (Pisa, Italy). Multiple test lighting configurations were designed using different LED luminaires and different settings of the luminaires. The test lighting configurations were evaluated by a restricted group of observers through a survey in order to individuate the most suitable solution, able to enhance the two artworks simultaneously and to provide a good visual experience for museum visitors

Infrared laser-based monitoring of the silane dissociation during deposition of silicon thin films

The silane dissociation efficiency, or depletion fraction, is an important plasma parameter by means of which the film growth rate and the amorphous-to-microcrystalline silicon transition regime can be monitored in situ. In this letter we implement a homebuilt quantum cascade laser-based absorption spectrometer to measure the silane dissociation efficiency in an industrial plasma-enhanced chemical vapor deposition system. This infrared laser-based diagnostic technique is compact, sensitive, and nonintrusive. Its resolution is good enough to resolve Doppler-broadened rotovibrational absorption lines of silane. The latter feature various absorption strengths, thereby enabling depletion measurements over a wide range of process conditions

Optical emission spectroscopy to diagnose powder formation in SiH4-H2 discharges

Silane and hydrogen discharges are widely used for the deposition of silicon thin film solar cells in large area plasmaenhanced chemical vapor deposition reactors. In the case of microcrystalline silicon thin film solar cells, it is of crucial importance to increase the deposition rate in order to reduce the manufacturing costs. This can be performed by using high silane concentration, and usually high RF power and high pressure, all favorable to powder formation in the discharge that generally reduces the deposition rate as well as the deposited material quality. This work presents a study of powder formation using time-resolved optical emission spectroscopy. It is shown that this technique is suitable to detect different regimes in powder formation ranging from powder free discharge to discharge producing large dust particles. Intermediate powder formation regimes include the formation of small silicon clusters at plasma ignition as well as cycle of powder growth and ejection out of the discharge, and both are observable by this low-cost and experimentally simple technique

Modeling enteric methane emission from beef cattle in Brazil: a proposed equation performed by principal component analysis and mixed modeling multiple regression.

Brazil has the largest commercial beef cattle herd in the world but does not have its own model to predict methane (CH4 ) emission. The aim of this study was to create the first empirical enteric CH4 emission equation from variables that describe the animal diet using a meta-analytical data from Brazilian scientific publications (n = 50, published from 2003 to 2012)