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The removal of a 75- to 90-nm-thick passivating silicon nitride antireflection coating from standard textured multicrystalline silicon photovoltaic wafers with a typical diffused 90-Ω/sq-emitter upon irradiation with near-infrared femtosecond laser pulses (790 nm central wavelength, 30 fs pulse duration) is studied experimentally. The laser irradiation areas are subsequently characterized by complementary optical microscopy, scanning electron microscopy and depth profiling chemical analyses using secondary ion mass spectrometry. The results clarify the thin-film femtosecond laser ablation scenario and outline the process windows for selective antireflection coating removal.
Serial interconnection of CIGSe thin film solar modules involves typically glass-side laser patterning of the molybdenum layer (P1 scribe). In this paper we present a working principle of P1 film side patterning. The investigated samples were sputter-deposited onto soda-lime glass substrates. For understanding the fundamental ablation behavior, two kinds of layer systems were studied: on the one hand monolayer systems which are compressively stressed and on the other hand bilayer systems, consisting of a tensile stressed layer on the substrate and a second layer on top. The film-side ablation process was studied using a nanosecond as well as a picosecond laser source. The influence of intrinsic stress was studied by XRD. Time resolved spectroscopy reveals the formation of plasma as important driving mechanism for ablation. It is shown that by proper adaption of the sputter conditions high-quality P1 film side patterning is achieved.
Towards an industrial laser doping process for the selective emitter using phosphoric acid as dopant
(2011)
Different laser supported approaches have already been realized, proving the great potential of laserdoped selective emitters (LDSE). However, it is challenging to establish a low-cost process by using pulsed laser tools. So far a single-step process only leads to satisfying results utilizing cw-lasers. In this paper we have examined a two-step process to produce laser-doped selective emitters on multicrystalline textured standard silicon photovoltaic wafers (90-Ω/sq-Emitter, SiN-antireflection coating (ARC)). The precise ARC removal by near-infrared fs-laser pulses (30 fs, 800 nm), and the doping of uncoated silicon wafers by ns-laser pulses (8 ns, 532 nm) were systematically investigated. In the fs-experiment, optimum conditions for ARC removal were identified. In the nsexperiments under suitable conditions (melting regime), the phosphorous concentration underneath the wafer surface was significantly increased and the sheet resistance was reduced by nearly a factor of two. Moreover, electrical measurements on fired metallization fingers deposited on the laser processed wafers showed low contact resistances. Hence, wafer conditioning with combined fs-laser- and ns-laser-processes are expected to be a promising technology for producing selective emitters.
Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon that can be observed on almost any material after the irradiation by linearly polarized laser beams, particularly when using ultrashort laser pulses with durations in the picosecond to femtosecond range. During the past few years significantly increasing research activities have been reported in the field of LIPSS, since their generation in a single-step process provides a simple way of nanostructuring and surface functionalization towards the control of optical, mechanical or chemical properties. In this contribution current applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting, the tailoring of surface colonization by bacterial biofilms, and the improvement of the tribological performance of nanostructured metal surfaces.
The wetting behavior of material surfaces can be controlled by surface structures. We functionalized case-hardened alloyed carbon steel to modify the wetting behavior using ultrashort laser pulses (fs- to ps-range). The laser processing was performed by scanning the laser beam across the surface of initially polished flat sample material. An experimental study of the laser processing parameters (peak fluence, scan velocity, line overlap) rendered an assignment of different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures, grooves, micro cones, etc.) possible. Analyzing the surface using optical as well as scanning electron microscopy allowed the identification of morphologies providing the optimum similarity to the natural skin of non-moisture havesting lizards. For mimicking skin structures of moisture-harvesting lizards, additionally a two-step laser processing strategy was established for realizing hierarchical microstructures. In this approach, micrometer-scaled capillaries (step 1) were superimposed by a laser-generated regular array of small dimples (step 2). Optical focus variation imaging measurements finally revealed the three dimensional topography of the laser processed surfaces derived from lizard skin structures. The functionality of these surfaces was analyzed in view of wetting and directional fluid transport properties. The results suggest possible applications of the laser-structured surfaces.
Surface nanostructures provide the possibility to create and tailor surface functionalities mainly via controlling their topography along with other chemical and physical material properties. One of the most appealing technologies for surface functionalization via micro- and nanostructuring is based on laser processing. This can be done either via direct contour-shaping of the irradiated material using a tightly focused laser beam or in a self-ordered way that allows employing larger laser beam diameters along with areal scanning to create a variety of laser-induced periodic surface structures (LIPSS). For the latter approach, particularly ultrashort pulsed lasers have recently pushed the borders across long-lasting limitations regarding the minimum achievable feature sizes and additionally boosted up the production times. This chapter reviews the plethora of recently investigated applications of LIPSS—for example, via imposing diffractive or plasmonic structural colors, the management of liquids and surface wetting properties, biomedical and bioinspired functionalities, beneficial effects in tribology for reducing friction and wear, the manipulation of optical scattering and absorption in photovoltaics, or the modification of magnetic or superconducting surface properties in other energy applications. The footprint of the LIPSS-based technology is explored in detail regarding the current state of industrialization, including an analysis of the market and associated LIPSS production costs.
Bacterial biofilms pose serious problems in medical and industrial settings. One of the major societal challenges lies in the increasing resistance of bacteria against biocides used in antimicrobial treatments, e.g., via overabundant use in medicine, industry, and agriculture or cleaning and disinfection in private households. Hence, new efficient bacteria-repellent strategies avoiding the use of biocides are strongly desired. One promising route to achieve bacteria-repellent surfaces lies in the contactless and aseptic large-area laser-processing of technical surfaces. Tailored surface textures, enabled by different laser-processing strategies that result in topographic scales ranging from nanometers to micrometers may provide a solution to this challenge. This article presents a current state-of-the-art review of laser-surface subtractive texturing approaches for controlling the biofilm formation for different bacterial strains and in different environments. Based on specific properties of bacteria and laser-processed surfaces, the challenges of anti-microbial surface designs are discussed, and future directions will be outlined.
The exciting properties of micro- and nano-patterned surfaces found in natural species hide a virtually endless potential of technological ideas, opening new opportunities for innovation and exploitation in materials science and engineering. Due to the diversity of biomimetic surface functionalities, inspirations from natural surfaces are interesting for a broad range of applications in engineering, including phenomena of adhesion, friction, wear, lubrication, wetting phenomena, self-cleaning, antifouling, antibacterial phenomena, thermoregulation and optics. Lasers are increasingly proving to be promising tools for the precise and controlled structuring of materials at micro- and nano-scales. When ultrashort-pulsed lasers are used, the optimal interplay between laser and material parameters enables structuring down to the nanometer scale. Besides this, a unique aspect of laser processing technology is the possibility for material modifications at multiple (hierarchical) length scales, leading to the complex biomimetic micro- and nano-scale patterns, while adding a new dimension to structure optimization. This article reviews the current state of the art of laser processing methodologies, which are being used for the fabrication of bioinspired artificial surfaces to realize extraordinary wetting, optical, mechanical, and biological-active properties for numerous applications. The innovative aspect of laser functionalized biomimetic surfaces for a wide variety of current and future applications is particularly demonstrated and discussed. The article concludes with illustrating the wealth of arising possibilities and the number of new laser micro/nano fabrication approaches for obtaining complex high-resolution features, which prescribe a future where control of structures and subsequent functionalities are beyond our current imagination.
Modern life and global communication would not be possible without technologically tailored thin films; they are omnipresent in daily life applications. In most cases, the films are deposited entirely at the carrying substrates in a specific processing step of the device or sample. In some cases, however, removal or modification must be performed locally, i.e., site-controlled and material selective through an additional laser processing step. For that ultrashort laser pulses with durations in the femtosecond and picosecond range can provide unique advantages and capabilities in industrially scalable schemes. This article reviews the current state of the research and corresponding industrial transfer related to the structuring of thin films by ultrashort pulsed lasers. It focuses on the pertinent historic developments, reveals the relevant physical and chemical effects, explores the ultimate limits, and discusses selected industrial and scientific applications.