Laser scribing is a promising technology for thin-film ablation in photovoltaic device manufacturing, particularly with non-conventional materials. This study explores copper oxides as alternative light absorbers due to their abundance and safe sourcing. Transition metal oxide (TMO) layers, like molybdenum oxide (MoO3), vanadium oxide (V2O5), and tungsten oxide (WO3), are investigated as selective contacts for advanced semiconductor devices. The research employs a high-powered fs laser (EKSPLA FemtoLux30, 30W, 1030 nm) with tunable pulse lengths (350 fs~1ps) and various wavelengths (1064, 532, and 355 nm) to determine the threshold ablation fluence and achieve optimal thin-film removal without substrate alteration. Diode isolation and electrical characteristics demonstrate the process's high quality.
We simulate laser ablation process of different metals in both ns and fs regime. Finite element method was implemented to numerically solve the thermal equations. Ablation has been modelled as a normal downwards mesh velocity. Ablation curves have been obtained for metals such as Ag, Cu and Al and oxides such as CuO; in ns regime we have also simulated multipulse operation. For ultrashort fs pulses, the Two-Temperature Model (TTM) needed to be applied. Improvements were made in an important thermal parameter of the TTM, the electron heat capacity, by solving the exact equations which give this parameter within the Free Electron Gas (FEG) model framework.
A study of the of laser peen forming of thin stainless steel metal foils (50 μm thick) using a solid-state ps-pulsed laser, emitting at a wavelength of 1064 nm was conducted. The dependence of the bending angle and the radius of curvature on the energy per pulse, the treated area, the distance between lines, and the repetition rate of the treatment is presented. The study also shows that the bending effect is local, and it cannot be scaled by increasing the repetition rate, because the increase in temperature relaxes the superficial stresses previously induced.
Laser-Induced Forward Transfer (LIFT) is a versatile technique, allowing the transfer of a wide range of materials, with no contact, and high accuracy. Here we show a complete study on the deposition by LIFT, focusing on the deposition of a high viscosity silver paste, from the LIFT process parametrization to the metallization and characterization of heterojunction silicon solar cells.
LIPSS as well as hierarchical structures were generated by applying picosecond laser irradiation on a stainless steel-304 probe in a confinement liquid medium. Periodicity modification from high to low spatial surface frequency LIPSS was observed by modifying the pulse repetition rate from 1.3 to 402 kHz at a constant fluence. One of the outcomes reported in this study was the wettability analysis of the processed area which yielded significative changes on the contact angle between a water drop and the treated surface showing a wetting transition from hydrophilicity to hydrophobicity as an effect of the multiple impact pulses.
Laser-Induced Forward Transfer (LIFT) is a direct-write laser technique for the transference of material in an enormous range of viscosities and rheological behaviors, from solid-state to low-density inks. Furthermore, LIFT enables the transference of small volumes of material (as low as picoliters) with a high lateral spatial resolution (down to a few micrometers) to produce printed patterns with great flexibility.
In this work, simulations using a finite-element model involving Phase Field tracking method are presented and compared with experimental results.
Specifically, two LIFT processes are studied: a modified model is used to reproduce the secondary effects (such as bulgy shapes and secondary jets) observed after several ms in Blister-Actuated LIFT (BA-LIFT) of glycerol/water mixtures, and a model for LIFT transference of high-viscosity metallic pastes employed to study the different regimes observed in experiments (non-transference, explosive, cluster, dot, and bridge transfer)
Laser-induced forward transfer (LIFT) is a fast, clean, non-contact metallization technique that allows the deposition of small volumes (down to picoliters) of a wide range of materials in a very precise and controlled way. In this work, we show a complete description of the metallization by LIFT using pulsed laser sources and a commercial silver-based paste. We include a description of the transference process and discuss the influence of the paste viscosity and the acceptor substrate roughness. To avoid the use of a standard paste-curing process in a furnace, a second laser process is used to cure the silver paste in a selective way, preventing any thermal damage in the materials below the paste or in other parts of the device. In summary, we show that the use of a LIFT technique allows the metallization of wide areas with high aspect ratio lines, that can be cured selectively, and present very good mechanical properties, being suitable for its use in flexible electronics applications.
Laser Direct Write techniques for printing applications of living material is currently a hot topic in different biomedical and engineering fields like tissue engineering, drug delivery, biosensing, etc. specialized groups in the field have been done to find and control the ideal conditions of printability, in order to maintaining unchanged the properties of the biological transferred material.
In this work we present a comprehensive study of the printability map of two of the most used biocompatible hydrogels, Sodium Alginate and Methylcellulose. We discuss the effect of hydrogel density, laser parameters influence, etc. using a blister assisted laser writing technique. In our approach we use a thick polyamide layer for blister generation, this presents huge advantages to limit the direct laser irradiation of the living material to be transferred.
In addition the physics of blister dynamics and droplet-jet formation is discussed by means of a combined study using numerical modeling of the process fluid dynamics and high speed imaging of the transfer.
Finally a particular example of advantages of the approach from the biological point of view is discussed presenting a cell viability study of Jurkat cell printing in the conditions discussed in the study
Laser induced forward transfer (LIFT) technique has been used for printing of various materials ranging from flexible metallic contacts to conductive silver lines. In this study, we are focusing on the printing of an industrial-grade silver paste formulated for the metalization of the front side of solar cells.
Printing of industrial silver pastes using the LIFT technique is challenging because the high viscosity of the silver paste allows only a small window of process parameters for reproducible and well-defined material transfer. In this work, we are examining the multiple-pulse effects during the printing of silver paste. Time-resolved imaging and characterization of the ejected silver paste voxels are performed to examine the influence of process parameters on the morphology of transferred paste dots and lines.
We have observed that by firing repeating laser pulses below the transfer energy threshold it is possible to print smaller volumes of paste, which yields an opportunity to print lines with higher resolution.
We also show that it is possible to print well-defined dots (voxels) of the paste using pulse energies near transfer threshold values. However, regarding the printing of lines, there is a strong interaction effect between adjacent voxels. This influence is so important that a distance between adjacent laser pulses threshold has been evaluated to print lines. The printing of single voxels has been achieved above the evaluated threshold value, while no printing could be achieved below the threshold. This distance threshold represents a limitation to the LIFT process of high viscosity pastes, which indicates that a compromise must be done between voxel size and laser frequency.
An advantage of laser crystallization over conventional heating methods is its ability to limit rapid heating and cooling to thin surface layers. In the present work, thin-film amorphous-silicon samples were irradiated with a continuous-wave green laser source. Laser irradiated spots were produced by using different laser powers and irradiation times. Micro-Raman spectroscopy was used to study the crystallization induced on the irradiated surface. Both laser peak power density and irradiation time are identified as key variables in the crystallization process, but within the parametric window considered, the enhancement of the crystalline factor, is more sensitive to the power density than to the irradiation time. The optimum parameters are then used for crystallizing a large sample area by means of overlapped laser scanned lines. Ellipsometric data experimentally show that the whole volume of a micron-thick sample is crystallized.
The main objective of this work is to adapt Laser Induced Forward Transfer (LIFT), a well-known laser direct writing technique for material transfer, to define metallic contacts (fingers and busbars) onto c-Si cells. A layer of a commercial silver paste (viscosity around 30-50 kcPs), with thickness in the order of tens of microns, is applied over a glass substrate using a coater.. 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 on the glass/silver interface producing a droplet of silver that it is transferred to the acceptor substrate. 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 voxels is studied using confocal microscopy. Long lines are printed with a scanner and their uniformity, width, and height are studied. Examples of metallization of large areas (up to 10 cm x 10 cm) over c-Si cells are presented.
An advantage of laser crystallization over conventional heating methods is its ability to limit rapid heating and cooling to
thin surface layers. Laser energy is used to heat the a-Si thin film to change the microstructure to poly-Si.
Thin film samples of a-Si were irradiated with a CW-green laser source. Laser irradiated spots were produced by using
different laser powers and irradiation times.
These parameters are identified as key variables in the crystallization process. The power threshold for crystallization is
reduced as the irradiation time is increased. When this threshold is reached the crystalline fraction increases lineally
with power for each irradiation time.
The experimental results are analysed with the aid of a numerical thermal model and the presence of two crystallization
mechanisms are observed: one due to melting and the other due to solid phase transformation.
Laser processing has been the tool of choice last years to develop improved concepts in contact formation for high efficiency crystalline silicon (c-Si) solar cells. New concepts based on standard laser fired contacts (LFC) or advanced laser doping (LD) techniques are optimal solutions for both the front and back contacts of a number of structures with growing interest in the c-Si PV industry. Nowadays, substantial efforts are underway to optimize these processes in order to be applied industrially in high efficiency concepts. However a critical issue in these devices is that, most of them, demand a very low thermal input during the fabrication sequence and a minimal damage of the structure during the laser irradiation process. Keeping these two objectives in mind, in this work we discuss the possibility of using laser-based processes to contact the rear side of silicon heterojunction (SHJ) solar cells in an approach fully compatible with the low temperature processing associated to these devices. First we discuss the possibility of using standard LFC techniques in the fabrication of SHJ cells on p-type substrates, studying in detail the effect of the laser wavelength on the contact quality. Secondly, we present an alternative strategy bearing in mind that a real challenge in the rear contact formation is to reduce the damage induced by the laser irradiation. This new approach is based on local laser doping techniques previously developed by our groups, to contact the rear side of p-type c-Si solar cells by means of laser processing before rear metallization of dielectric stacks containing Al2O3. In this work we demonstrate the possibility of using this new approach in SHJ cells with a distinct advantage over other standard LFC techniques.
This work investigates the influence of the laser wavelength on laser doping (LD) and laser-fired contact (LFC)
formation in solar cell structures. We compare the results obtained using the three first harmonics (corresponding to
wavelengths of 1064 nm, 532 nm and 355 nm) of fully commercial solid state laser sources with pulse width in the ns
range. The discussion is based on the impact on the morphology and electrical characteristics of test structures.
In the case of LFC the study includes the influence of different passivation layers and the assessment of the process
quality through electrical resistance measurements of an aluminium single LFC point for the different wavelengths.
Values for the normalized LFC resistance far below 1.0 mΩcm2 have been obtained, with better results at shorter
wavelengths.
To assess the influence of the laser wavelength on LD we have created n+ regions into p-type c-Si wafers, using a dry
LD approach to define punctual emitters. J-V characteristics show exponential trends at mid-injection for a broad
parametric window in all wavelengths, with local ideality factors well below 1.5.
In both processes the best results have been obtained using green (532 nm) and, specially, UV (355 nm). This indicates
that to minimize the thermal damage in the material is a clear requisite to obtain the best electrical performance, thus
indicating that UV laser shows better potential to be used in high efficiency solar cells.
In this work, we report the optical properties of Tm3+, Er3+, and Tm3+-Er3+ codoped tellurite TeO2-WO3-PbO glasses for
different Er3+ and Tm3+ concentrations. Judd-Ofelt intensity parameters have been determined to calculate the radiative
transition probabilities and radiative lifetimes of excited states of Tm3+ and Er3+ ions. Luminescence spectra and
lifetimes were measured under 793 nm and 800 nm excitations. The infrared emission of Tm3+ at 1470 nm is broader by
around 30 nm and the stimulated emission cross section twice if compared to fluoride glasses used for S-band
amplifiers. Moreover, a broad emission from 1350 to 1600 nm with a full width at half-maximum of ~ 160 nm is
obtained by codoping the glass with Tm2O3 an Er2O3 which suggests these glasses could be promising materials as
broadband light sources and broadband amplifiers for wavelength-division-multiplexing (WDM) transmission systems.
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