Laser ablation modelling of aluminium, silver and crystalline silicon for applications in photovoltaic technologies

Laser material processing is being extensively used in photovoltaic applications for both the fabrication of thin film modules and the enhancement of the crystalline silicon solar cells. The two temperature model for thermal diffusion was numerically solved in this paper. Laser pulses of 1064, 532 or 248 nm with duration of 35, 26 or 10 ns were considered as the thermal source leading to the material ablation. Considering high irradiance levels (108–109 W cm−2), a total absorption of the energy during the ablation process was assumed in the model. The materials analysed in the simulation were aluminium (Al) and silver (Ag), which are commonly used as metallic electrodes in photovoltaic devices. Moreover, thermal diffusion was also simulated for crystalline silicon (c-Si). A similar trend of temperature as a function of depth and time was found for both metals and c-Si regardless of the employed wavelength. For each material, the ablation depth dependence on laser pulse parameters was determined by means of an ablation criterion. Thus, after the laser pulse, the maximum depth for which the total energy stored in the material is equal to the vaporisation enthalpy was considered as the ablation depth. For all cases, the ablation depth increased with the laser pulse fluence and did not exhibit a clear correlation with the radiation wavelength. Finally, the experimental validation of the simulation results was carried out and the ability of the model with the initial hypothesis of total energy absorption to closely fit experimental results was confirmed.

Laser induced forward transfer of silver pastes for printing of fingers in c-si cells.

The main objective of this work is to adapt the Laser Induced Forward Techniques (LIFT), a well- known laser direct writing technique for material transfer, to define metallic contacts (fingers and busbars) onto c-Si cells. The silver paste (with viscosity around 30-50 kcPs) is applied over a glass substrate using a coater. The thickness of the paste can be control changing the deposit parameters. The glass with the silver paste is set at a controlled gap over the c-Si cell. A solid state pulsed laser (532 nm) is focused at the glass/silver interface producing a droplet of silver that it is transferred to the c-Si cell. A scanner is used to print lines. The process parameters (silver paste thickness, gap and laser parameters -spot size, pulse energy and overlapping of pulses) are modified and the morphology of the lines is studied using confocal microscopy. Long lines are printed and the uniformity (in thickness and height) is studied. Some examples of metallization of larger areas (up to 10 cm x 10 cm) are presented.

National survey of speeding and other unsafe driving actions. Volume I: methodology.

National Highway Traffic Safety Administration, Office of Research and Traffic Records, Washington, D.C.

An investigation of used car safety: final report. Volume I-summary and program plan.

Mode of access: Internet.

Still Life with a Silver Jug and a Porcelain Bowl

Willem Kalf; 2 ft. 5 1/16 in.x 2 ft. 3 3/64 in.; oil on canvas

Exploration diamond drilling in the Boulder batholith, Jefferson and Silver Bow Counties, Montana /

Radiometric logging of the drill holes was accomplished by means of a Geiger counter-type probe. Samples for chemical assay were selected after checking the core with a Geiger counter and correlation with the radiometric logging record. The exploration project did not disclose significant amounts of ore-grade material although encouraging indications were found at two different properties.

Chisat I, extension and validation of NOAA's REPEX procedures for habitat diving : a Chinese-American collaboration /

"October 1990."

Living on other people's means; or, The history of Simon Silver.

Attributed to Hannah Farnham Sawyer Lee.

Contributions to economic geology (short papers and preliminary reports), 1931-32 : Part I. - Metals and nonmetals except fuels /

Mode of access: Internet.