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.
Transition metal oxide (TMOs) layers have interesting properties as selective contacts for novel semiconductor devices. Especially, oxides of molybdenum (MoO3), vanadium (V2O5), and tungsten (WO3) show good behaviour acting as front hole-selective contacts for n-type crystalline silicon heterojunction solar cells. Laser scribing has been widely used for thin-film ablation and seems the appropriate technology for device manufacturing with such non-conventional materials. In this work, we study the laser scribing of non-stoichiometric evaporated WOx, VOx, and MoOx films with three different wavelengths (1064, 532, and 355 nm) with pulse duration in the ns and ps regimes. The selection of the proper laser source allows a wide parametric window, with complete removal of the TMO films and no alteration of the silicon substrate. The results on the isolation of diodes and their electrical characteristics show the quality of the laser scribing processes.
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.
Achieving functionalized artificial skin with immune response would solve an important problem when treating burn patients with larger skin transplants, since the skin is the main immune barrier of the human body and until now these models have lacked immune response. Furthermore, with the proper biological approach, we could obtain a generic skin suitable for transplantation to patients with different major histocompatibility complex (MHC). This work presents an original method to achieve this goal by creating cylindrical pore-like structures with laser, where subsequently immune cells are included using a BA-LIFT (Blister Actuated Laser Induced Forward Transfer) technique in a co-culture with the treated skin, in order to assess their engraftment to the artificial skin.
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 bioprinting is a powerful tool in many biological fields due to its versatility in placing and construct different geometries of biological materials. The high accuracy and non-destructive nature of this method can be applied to the study of complex biological systems. In particular, single cell laser bioprinting helps to understand the relationships between cells and their local environment. Immunology is a transversal field that is governed by a complex network of genetic and signalling pathways subtending a network of interacting cells. In this context, mobility of the cells in a network along with their situation and the gene products they interact with, plays an important roll in the behaviour of the immune system. In this work we use a laser induced forward transfer blister assisted (BALIFT) approach to assess these cell-cell interaction and mobility in vitro. This method helps to understand properly the role of a cell in such networks to increase our knowledge of the immune system response. This work presents BALIFT bioprinting of single hematopoietic cells and chemoattractant proteins with high spatial resolution. In particular NK cells (natural killer), T-lymphocyte and chemokines and cytokine molecules are printed in specific patterns to study cell-cell and cell-environment interaction and cell migration. Whereby placing cellular components on a matrix previously designed on demand allow us to test the molecular interactions between lymphocytes and pathogens; as well as the generation of two-dimensional structures printed ad hoc in order to study the mechanisms of mobilization of immune system cells.
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
Publisher’s Note: This conference presentation, originally published on 4/19/17, was withdrawn per author request.
The immune system is a very complex system that comprises a network of genetic and signaling pathways subtending a network of interacting cells. The location of the cells in a network, along with the gene products they interact with, rules the behavior of the immune system. Therefore, there is a great interest in understanding properly the role of a cell in such networks to increase our knowledge of the immune system response. In order to acquire a better understanding of these processes, cell printing with high spatial resolution emerges as one of the promising approaches to organize cells in two and three-dimensional patterns to enable the study the geometry influence in these interactions. In particular, laser assisted bio-printing techniques using sub-nanosecond laser sources have better characteristics for application in this field, mainly due to its higher spatial resolution, cell viability percentage and process automation. This work presents laser assisted bio-printing of antigen-presenting cells (APCs) in two-dimensional geometries, placing cellular components on a matrix previously generated on demand, permitting to test the molecular interactions between APCs and lymphocytes; as well as the generation of two-dimensional structures designed ad hoc in order to study the mechanisms of mobilization of immune system cells. The use of laser assisted bio-printing, along with APCs and lymphocytes emulate the structure of different niches of the immune system so that we can analyse functional requirement of these interaction.
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.
Light confinement strategies play a crucial role in the performance of thin-film (TF) silicon solar cells. One way to reduce the optical losses is the texturing of the transparent conductive oxide (TCO) that acts as the front contact. Other losses arise from the mismatch between the incident light spectrum and the spectral properties of the absorbent material that imply that low energy photons (below the bandgap value) are not absorbed, and therefore can not generate photocurrent. Up-conversion techniques, in which two sub-bandgap photons are combined to give one photon with a better matching with the bandgap, were proposed to overcome this problem. In particular, this work studies two strategies to improve light management in thin film silicon solar cells using laser technology. The first one addresses the problem of TCO surface texturing using fully commercial fast and ultrafast solid state laser sources. Aluminum doped Zinc Oxide (AZO) samples were laser processed and the results were optically evaluated by measuring the haze factor of the treated samples. As a second strategy, laser annealing experiments of TCOs doped with rare earth ions are presented as a potential process to produce layers with up-conversion properties, opening the possibility of its potential use in high efficiency solar cells.
It is well known that lasers have helped to increase efficiency and to reduce production costs in the photovoltaic (PV) sector in the last two decades, appearing in most cases as the ideal tool to solve some of the critical bottlenecks of production both in thin film (TF) and crystalline silicon (c-Si) technologies. The accumulated experience in these fields has brought as a consequence the possibility of using laser technology to produce new Building Integrated Photovoltaics (BIPV) products with a high degree of customization. However, to produce efficiently these personalized products it is necessary the development of optimized laser processes able to transform standard products in customized items oriented to the BIPV market. In particular, the production of semitransparencies and/or freeform geometries in TF a-Si modules and standard c-Si modules is an application of great interest in this market. In this work we present results of customization of both TF a-Si modules and standard monocrystalline (m-Si) and policrystalline silicon (pc-Si) modules using laser ablation and laser cutting processes. A discussion about the laser processes parameterization to guarantee the functionality of the device is included. Finally some examples of final devices are presented with a full discussion of the process approach used in their fabrication.
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.
In this paper we present an original approach to estimate the heat affected zone in laser scribing processes for photovoltaic applications. We used high resolution IR-VIS Fourier transform spectrometry at micro-scale level for measuring the refractive index variations at different distances from the scribed line, and discussing then the results obtained for a-Si:H layers irradiated in different conditions that reproduce standard interconnection parameters. In order to properly assess the induced damage by the laser process, these results are compared with measurements of the crystalline state of the material using micro-Raman techniques. Additionally, the authors give details about how this technique could be used to feedback the laser process parametrization in monolithic interconnection of thin film photovoltaic devices based on a-Si:H.
Hydrogenated amorphous silicon has been widely studied last years, both from the basic research and industrial points of view, due to the important set of potential applications that this material offers, ranging from Thin Films Transistors (TFTs) to solar cells technologies. In different fabrication steps of a-Si:H based devices, laser sources have been used as appropriate tools for cutting, crystallising, contacting, patterning, etc., and more recent research lines are undertaking the problem of a-Si:H selective laser ablation for different applications.
The controlled ablation of photovoltaic materials with minimum debris and small heat affected zone with low processing costs, is one of the main difficulties for the successful implementation of laser micromachining as competitive technology in this field. This work presents a detailed study of a-Si:H laser ablation in the ns regime. Ablation curves are measured and fluence thresholds are determined. Additionally, and due to the improved performance in optolectronic properties associated to the nanocrystalline silicon (nc-Si:H), some samples of this material have been also studied.
Position detectors are useful for alignment and orientation sensing. Charge-coupled devices (CCDs) are used in small-area systems. Four-quadrant diodes are a low-cost, limited-accuracy alternative. In cases where either large area or reliability under harsh conditions are required, thin-film-silicon sensors may become the only reasonable choice. The paper proposes a simple structure for making such devices, describes the first experiments and discusses the key issues faced, with emphasis on laser scribing.
Laser micromachining of semiconductor and Transparent Conductive Oxides (TCO) materials is very important for the practical applications in photovoltaic industry. In particular, a problem of controlled ablation of those materials with minimum of debris and small heat affected zone is one of the most vital for the successful implementation of laser micromachining.
In particular, selective ablation of thin films for the development of new photovoltaic panels and sensoring devices based on amorphous silicon (a-Si) is an emerging field, in which laser micromachining systems appear as appropriate tools for process development and device fabrication. In particular, a promising application is the development of purely photovoltaic position sensors. Standard p-i-n or Schottky configurations using Transparent Conductive Oxides (TCO), a-Si and metals are especially well suited for these applications, appearing selective laser ablation as an ideal process for controlled material patterning and isolation.
In this work a detailed study of laser ablation of a widely used TCO, Indium-tin-oxide (ITO), and a-Si thin films of different thicknesses is presented, with special emphasis on the morphological analysis of the generated grooves. The profiles of ablated grooves have been studied in order to determine the best
processing conditions, i.e. laser pulse energy and wavelength, and to asses this technology as potentially competitive to standard photolithographic processes.
The encouraging results obtained, with well defined ablation grooves having thicknesses in the order of 10 μm both in ITO and a-Si, open up the possibility of developing a high-performance double Schottky photovoltaic matrix position sensor.
Laser micromachining techniques are among the most promising fabrication processes in strategic industrial fields. Although lasers systems have been widely applied last twenty years in semiconductor industry for microfabrication process development, the current availability of new excimer and Diode Pumped Solid State Lasers (DPSS) sources are extending the applications fields of laser microprocessing. Nowadays MEMs, fluidic devices, advanced sensors and biomedical devices and instruments are among the more promising developments of this technology. Nevertheless the fast progress of this technology has brought as a consequence the building up of specific laser based machines for each process of interest (most of them until now strictly 2D), and an important gap has been generated, from the fabrication point of view, in fully 3D potential applications. In this work, the conception, design and first results of a fully automatized 3D laser micromachining workstation, based on the main concept of flexibility, is presented. This system integrates two UV laser sources, excimer and DPSS in ns pulse regime, and an advanced positioning system (with six degrees of freedom) for complex parts machining. Several examples of first results obtained with this system, including processing of semiconductors for sensoring and photovoltaic applications, organic materials for biomedical devices and metallic materials for different strategic industrial sectors are presented.
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