Moderne optoelektronische Dünnfilmapplikationen erfordern den Einsatz effizienter großflächiger Elektrodensysteme, die einerseits über sehr gute Leitfähigkeitseigenschaften verfügen und andererseits eine hohe Transparenz in einem breiten Wellenlängenspektrum aufweisen. Momentan wird für derartige Anwendungen zum Großteil der Werkstoff Indiumzinnoxid (ITO) eingesetzt, dessen Hauptbestandteil Indium nur in geringen Mengen auf der Erde vorkommt. Für die Erhaltung der Marktfähigkeit und zur Weiterentwicklung der Dünnschichtelektronik ist es nötig, dieses Ressourcenproblem zu lösen. Eine Möglichkeit zur Substitution von ITO ist die Verwendung dünner metallischer Filme als transparente Elektroden. Die vorliegende Dissertationsschrift untersucht in diesem Zusammenhang die Anwendung der Direkten Laserinterferenzstrukturierung (DLIP). Um hinreichend große optische Transparenz bei entsprechender elektrischer Leitfähigkeit zu erhalten, werden Dünnschichtensysteme aus Kupfer, Aluminium, Chrom und Silber mit verschiedenen periodischen Lochmustern zwischen 1,5-2,7 µm perforiert. Im Anschluss werden die bearbeiteten Probenkörper hinsichtlich ihrer optischen, elektrischen und topografischen Eigenschaften vermessen. Die umfangreichen gewonnenen Daten werden in einer Auswertung zusammengefasst und mit Resultaten aus numerischen Modellrechnungen verglichen. Neben den Ergebnissen zur Effizienzsteigerung der Dünnfilme untersucht die vorliegende Arbeit die laserinduzierte Ablationsdynamik metallischer Filme auf Glassubstrat zwischen 5-40 nm Schichtdicke.:1 Einleitung 1 2 Theoretische Grundlagen 4 2.1 Verfahren zur Herstellung von Dünnschicht-Elektroden 4 2.1.1 Verdampfungsverfahren 4 2.1.2 Sputterverfahren 5 2.1.3 Metallorganische Gasphasenepitaxie – MOCVD 6 2.2 Schichtwachstum von Metallfilmen in PVD-Verfahren 7 2.3 Elektrische Eigenschaften von Dünnschicht-Elektroden 9 2.3.1 Mechanismen der elektrischen Leitung in Festkörpern 9 2.3.2 Elektrische Charakteristika von Indiumzinnoxid-Schichten 10 2.3.3 Elektrische Charakteristika dünner Metallschichten 10 2.4 Optische Eigenschaften dünner Schichten 13 2.4.1 Wechselwirkung von Licht mit Materie 13 2.4.2 Lichtmanipulation durch periodische Strukturen 14 2.4.3 Optische Eigenschaften transparenter ITO-Schichten 17 2.4.4 Optische Eigenschaften metallischer Dünnschichten 18 2.5 Grundlagen lasergestützter Bearbeitungsmethoden 19 2.5.1 Materialablation durch gepulste Laserstrahlung 19 2.5.2 Theoretische Grundlagen zur Bestimmung der Ablationsschwelle 21 2.6 Verfahren zur Mikrostrukturierung von Oberflächen 22 2.6.1 Elektronenstrahl-Lithographie 23 2.6.2 Sequentielles Laserstrukturieren 24 2.6.3 Strukturieren mit Laserinterferenz 25 2.7 Aktueller Forschungsstand zur DLIP dünner Metallschichten 29 2.7.1 DLIP metallischer Filme mit Nanosekunden-Pulsen 29 2.7.2 DLIP metallischer Filme mit Pikosekunden-Pulsen 35 3 Experimentelle Arbeit 37 3.1 Entwicklung numerischer Rechenmodelle 37 3.1.1 Modellierung des Interferenzvolumens 37 3.2 Thermische Simulationen 38 3.3 Experimente und Versuchsanordnungen 42 3.3.1 Verwendete Lasersysteme 42 3.3.2 Vorgehensweise zur Bestimmung der Ablationsschwellwerte 42 3.3.3 Laser-Annealing metallischer Dünnschichten 43 3.3.4 Direkte Laserinterferenzstrukturierung 44 3.3.5 Übersicht der verwendeten Dünnfilmsubstrate 47 3.3.6 Mess- und Analysemethoden 49 4 Auswertung und Diskussion 55 4.1 Ermittlung der Ablationsschwellwerte 55 4.1.1 Ablationsschwellwerte bei Nanosekunden-Pulsen 55 4.1.2 Ablationsschwellwerte bei Pikosekunden-Pulsen 58 4.2 Charakterisierung unbehandelter Dünnschichten 58 4.2.1 Topographische Eigenschaften unbehandelter Metalldünnschichten 58 4.2.2 Optische und Elektrische Eigenschaften unbehandelter metallischer Filme 59 4.3 Charakterisierung lasergeglühter Metalldünnschichten 60 4.3.1 Optische Eigenschaften lasergeglühter Metallfilme 60 4.3.2 Elektrische Eigenschaften lasergeglühter Metallschichten 61 4.3.3 Schlussfolgerungen aus den Annealing-Experimenten 63 4.4 Ergebnisse der Modellrechnungen 63 4.4.1 Mathematische Simulation der Interferenzeigenschaften 63 4.5 Charakterisierung DLIP-strukturierter Metalldünnschichten 67 4.5.1 DLIP-Strukturierung von Silberdünnschichten ns-Pulsen 67 4.5.2 DLIP-Strukturierung von Silberdünnschichten mit ps-Pulsen 71 4.5.3 DLIP-Strukturierung von Kupferdünnschichten mit ns-Pulsen 77 4.5.4 DLIP-Strukturierung von Kupferdünnschichten mit ps-Pulsen 89 4.5.5 DLIP-Strukturierung von Aluminiumdünnschichten mit ns-Pulsen 93 4.5.6 DLIP-Strukturierung von Aluminiumdünnschichten mit ps-Pulsen 106 4.5.7 DLIP-Strukturierung von Chromdünnschichten mit ns-Pulsen 111 4.5.8 Charakterisierung DLIP-strukturierter Vielschicht-Substrate 116 4.6 Optische Charakterisierung 118 4.6.1 Optische Eigenschaften mittels ns-Pulsen strukturierter Filme 119 4.6.2 Optische Eigenschaften mittels ps-Pulsen strukturierter Filme 127 4.6.3 Optische Charakterisierung DLIP-strukturierter Vielschicht-Substrate 129 4.7 Elektrische Eigenschaften 131 4.7.1 Schichtwiderstand DLIP-strukturierter Metallelektroden 131 4.7.2 Schichtwiderstand DLIP-strukturierter Vielschicht-Elektroden 140 5 Zusammenfassung 144 6 Ausblick 149 7 Literaturverzeichnis 150 8 Anhang 161

In the past 15 years, many efforts were made to create functionalized artificial surfaces showing special anti-bacterial and anti-biofouling properties. Thereby, the topography of medical relevant materials plays an important role. However, the targeted fabrication of promising surface structures like hole-, lamella- and pyramid-like patterns with feature sizes in the sub-micrometer range in a one-step process is still a challenge. Optical and e-beam lithography, molding and selfassembly layers show a great potential to design topographies for this purpose. At the same time, most of these techniques are based on sequential processes, require masks or molds and thus are very device relevant and time consuming. In this work, we present the Direct Laser Interference Patterning (DLIP) technology as a capable method for the fast, flexible and direct fabrication of periodic micrometer- and submicrometer structures. This method offers the possibility to equip large plain areas and curved devices with 1D, 2D and 3D patterns. Simple 1D (e.g. lines) and complex 3D (e.g. lamella, pillars) patterns with periodic distances from 0.5 μm to 5 μm were fabricated on polymeric materials (polyimide, polystyrene). Subsequently, we characterized the adhesion behavior of Staphylococcus epidermidis and S. aureus bacteria under in vitro and in vivo conditions. The results revealed that the topographies have a significant impact on bacteria adhesion. On the one side, one-dimensional line-like structures especially with dimensions of the bacteria enhanced microbe attachment. While on the other hand, complex three-dimensional patterns prevented biofilm formation even after implantation and contamination in living organisms.

Surfaces equipped with periodic patterns with feature sizes in the micrometer, submicrometer and nanometer range present outstanding surface properties. Many of these surfaces can be found on different plants and animals. However, there are few methods capable to produce such patterns in a one-step process on relevant technological materials. Direct laser interference patterning (DLIP) provides both high resolution as well as high throughput. Recently, fabrication rates up to 1 m²·min-1 could be achieved. However, resolution was limited to a few micrometers due to typical thermal effects that arise when nanosecond pulsed laser systems are used. Therefore, this study introduces an alternative to ns-DLIP for the fabrication of multi-scaled micrometer and submicrometer structures on nickel surfaces using picosecond pulses (10 ps at a wavelength of 1064 nm). Due to the nature of the interaction process of the metallic surfaces with the ultrashort laser pulses, it was not only possible to directly transfer the shape of the interference pattern intensity distribution to the material (with spatial periods ranging from 1.5 μm to 5.7 μm), but also to selectively obtain laser induce periodic surface structures with feature sizes in the submicrometer and nanometer range. Finally, the structured nickel sleeves are utilized in a roll-to-roll hot embossing unit for structuring of polymer foils. Processing speeds up to 25 m·min-1 are reported.

In this work, the mesh-free smoothed particle hydrodynamics (SPH) method is applied in the modelling of the direct laser interference patterning (DLIP) of metal surfaces. The DLIP technique allows the fabrication of periodic microstructures on technical surfaces using nanosecond laser pulses. Here, the interference of two coherent partial beams with a sinusoidal energy density distribution of the interference pattern is concerned, which is employed to generate line-like surface structures. However, the mechanisms effective during nanosecond pulsed DLIP of metals are not yet fully understood. The physical phenomena occurring due to the interaction of laser radiation with metallic materials are first considered and the governing differential equations are stated. The fundamentals of the SPH method and the approaches to the numerical treatment of the conservation equations are presented. Physical processes relevant to the modelling of laser material processing are solved by suitable SPH techniques, i.e. the approximations are verified with respect to test problems with analytical or known numerical solutions. Consequently, the SPH method is used to devise a thermal model of the DLIP process, considering the absorption of the laser radiation, the heat conduction into the workpiece and the latent heat of involved phase changes. This model is extended to compute the melt pool convection during DLIP, which is driven by surface tension gradients due to temperature gradients. For this purpose, an incompressible SPH (ISPH) method is used, representing a novel approach to the modelling of the laser-induced melt pool flow. The numerical model is employed to perform simulations of DLIP on metal substrates. Firstly, the thermal simulation of the single pulse patterning of stainless steel is in good agreement with experimental results. The application of DLIP to stainless steel and aluminium is then simulated by the comprehensive model including the melt pool flow. Moreover, this model is further extended to consider the non-linear temperature dependence of surface tension, as in liquid steel in the presence of a surface active element. The simulation results reveal a distinct behaviour of stainless steel and aluminium substrates. A markedly deeper melt pool and considerable velocity magnitudes of the thermocapillary convection at the melt surface are computed for DLIP of aluminium. In contrast, the melt pool flow is less pronounced during DLIP of stainless steel, whereas higher surface temperatures are predicted. Hence the Marangoni convection is a conceivable effective mechanism during the structuring of aluminium at moderate energy density. The different character of the melt pool convection during DLIP of stainless steel and aluminium is corroborated by experimental observations. Furthermore, the simulations for stainless steel with different sulphur content indicate distinct melt pool flow patterns and support the explanation of the microstructures found after DLIP experiments. The role of vapourisation and the induced recoil pressure in the microstructure evolution due to DLIP on metal substrates at elevated fluences could be prospectively investigated. In this regard, the consideration of the melt pool surface deformation in the ISPH algorithm, and particularly a suitable pressure boundary condition, is required.:I The research problem 1 Motivation 2 Modelling of laser material processing 2.1 Interaction of laser radiation with materials 2.1.1 Absorption of laser radiation 2.1.2 Heat conduction and phase change 2.1.3 Molten pool convection 2.1.4 Vapourisation regime 2.2 Mathematical modelling of laser material interaction 2.2.1 Conservation equations in Lagrangian formulation 2.2.2 Influence of surface tension 3 State of the art in laser microprocessing and the SPH method 3.1 Laser microprocessing 3.2 Simulation of direct laser interference patterning 3.3 The mesh-free smoothed particle hydrodynamics method 3.3.1 Fundamental approximations and kernel function 3.3.2 Particle distribution and interaction length 3.3.3 Approximation of derivatives 3.3.4 Treatment of boundaries 3.3.5 Neighbourhood search 3.4 Numerical modelling of laser material processing by SPH II SPH model development for direct laser interference patterning 4 SPH modelling of heat transfer and fluid flow 4.1 Solution of the heat diffusion equation 4.2 Formulation of equations governing fluid flow 4.2.1 Equation of continuity 4.2.2 Approximation of pressure gradient term 4.2.3 Treatment of viscosity 4.3 Weakly compressible SPH method for solving fluid flow 4.3.1 Particle motion 4.3.2 Time integration 4.3.3 Time step criteria 4.4 Incompressible SPH method for solving fluid flow 4.4.1 Time integration 4.4.2 Discrete incompressible SPH algorithm 4.4.3 Time step criteria 4.5 Simulation of thermal fluid flow using ISPH 4.5.1 Semi-implicit time integration 4.5.2 Solution of the pressure Poisson equation 5 Verification of the SPH implementation 5.1 Transient heat conduction in laser-irradiated plate 5.1.1 Problem description 5.1.2 Dimensionless formulation 5.1.3 Numerical solution and results 5.2 Viscous flow 5.2.1 Couette flow 5.2.2 Poiseuille flow 5.3 Thermal convection 5.3.1 Natural convection in a square cavity 5.3.2 Rayleigh--Marangoni--Bénard convection in liquid aluminium 6 SPH model of direct laser interference patterning 6.1 Characteristics of the process 6.2 Thermal model 6.2.1 Non-dimensionalisation 6.2.2 Numerical solution of governing equation 6.2.3 Verification of the computation 6.2.4 Numerical test 6.3 Thermofluiddynamic model 6.3.1 Non-dimensionalisation 6.3.2 Numerical solution of governing equations 6.3.3 Discretisation 6.3.4 Resolution independence study 7 SPH simulation of direct laser interference patterning 7.1 Thermal model 7.1.1 DLIP experiments on stainless steel substrates 7.1.2 Thermal simulation of DLIP on steel substrate 7.2 Thermofluiddynamic model 7.2.1 Material properties and simulation parameters 7.2.2 Numerical results for steel substrate 7.2.3 Numerical results for aluminium substrate 7.2.4 Discussion and comparison with experiments 7.3 Extended thermofluiddynamic model 7.3.1 Model parameters 7.3.2 Influence of sulphur content on DLIP of stainless steel 8 Conclusions and outlook Bibliography / In dieser Arbeit wird die direkte Laserinterferenzstrukturierung (Direct Laser Interference Patterning, DLIP) von Metallen mit der netzfreien Smoothed Particle Hydrodynamics (SPH) Methode modelliert. Das DLIP-Verfahren ermöglicht die Fertigung periodischer Mikrostrukturen auf technischen Oberflächen mit Nanosekunden-Laserpulsen. Hier wird die Zweistrahlinterferenz mit einer sinusförmigen Energiedichteverteilung des Interferenzmusters behandelt, die linienförmige Oberflächenstrukturen erzeugt. Die bei der direkten Interferenzstrukturierung von Metallen mit Nanosekunden-Laserpuls wirksamen Mechanismen sind jedoch noch nicht verstanden. Die aufgrund der Wechselwirkung von Laserstrahlung mit metallischen Werkstoffen auftretenden physikalischen Phänomene werden zuerst betrachtet und die sie bestimmenden Differentialgleichungen angegeben. Die Grundlagen der SPH-Methode sowie deren Herangehensweisen an die numerische Behandlung der Erhaltungsgleichungen werden vorgestellt. Für die Modellierung der Lasermaterialbearbeitung relevante physikalische Vorgänge werden mittels geeigneter SPH-Ansätze gelöst, d. h. anhand von Testproblemen mit bekannter Lösung verifiziert. Das mit SPH zunächst erstellte thermische Modell des DLIP-Prozesses berücksichtigt die Absorption der Laserstrahlung, die Wärmeleitung im Werkstück und die Enthalpien der Phasenübergänge. Das Modell wird zur Berechnung der Schmelzbadströmung bei der DLIP-Anwendung, angetrieben von Oberflächenspannungsgradienten verursacht durch Temperaturgradienten, erweitert. Hierbei wird eine inkompressible SPH (ISPH) Methode eingesetzt, in der Simulation laserinduzierter Schmelzbäder ein neuartiger Ansatz. Mit dem numerischen Modell werden Simulationen des DLIP-Verfahrens für metallische Substrate durchgeführt. Die thermische Simulation der Strukturierung von Edelstahl stimmt gut mit einem Experiment überein. Weiterhin wird die Anwendung von DLIP auf Edelstahl und Aluminium mit dem thermofluiddynamischen Modell simuliert. Außerdem wird das Modell um eine nichtlinear temperaturabhängige Oberflächenspannung, wie sie für Stahlschmelze in Anwesenheit eines oberflächenaktiven Elements vorliegt, ergänzt. Die Simulationen zeigen ein verschiedenes Verhalten von Edelstahl und Aluminium. Bei der Strukturierung von Aluminium treten ein deutlich tieferes Schmelzbad und erhebliche Geschwindigkeitsbeträge der thermokapillaren Konvektion an der Schmelzeoberfläche auf. Hingegen ist die Strömung bei der DLIP-Anwendung auf Edelstahl schwächer ausgeprägt und höhere Oberflächentemperaturen werden erreicht. Die Marangoni-Konvektion ist daher ein wirksamer Schmelzeverdrängungsmechanismus bei der Strukturierung von Aluminium mit moderater Energiedichte. Die unterschiedliche Schmelzbadströmung für die beiden Werkstoffe wird durch experimentelle Beobachtungen bestätigt. In Abhängigkeit des Schwefelgehalts von Edelstahl zeigen Simulationen verschiedene Strömungsmuster im Schmelzbad und unterstützen die Erklärung experimentell festgestellter Mikrostrukturen. Die Untersuchung der Wirkung der Verdampfung und des induzierten Rückstoßdruckes auf die Strukturausbildung bei höheren Fluenzen erfordert die Berücksichtigung der Oberflächendeformation sowie eine geeignete Druckrandbedingung im ISPH-Algorithmus.:I The research problem 1 Motivation 2 Modelling of laser material processing 2.1 Interaction of laser radiation with materials 2.1.1 Absorption of laser radiation 2.1.2 Heat conduction and phase change 2.1.3 Molten pool convection 2.1.4 Vapourisation regime 2.2 Mathematical modelling of laser material interaction 2.2.1 Conservation equations in Lagrangian formulation 2.2.2 Influence of surface tension 3 State of the art in laser microprocessing and the SPH method 3.1 Laser microprocessing 3.2 Simulation of direct laser interference patterning 3.3 The mesh-free smoothed particle hydrodynamics method 3.3.1 Fundamental approximations and kernel function 3.3.2 Particle distribution and interaction length 3.3.3 Approximation of derivatives 3.3.4 Treatment of boundaries 3.3.5 Neighbourhood search 3.4 Numerical modelling of laser material processing by SPH II SPH model development for direct laser interference patterning 4 SPH modelling of heat transfer and fluid flow 4.1 Solution of the heat diffusion equation 4.2 Formulation of equations governing fluid flow 4.2.1 Equation of continuity 4.2.2 Approximation of pressure gradient term 4.2.3 Treatment of viscosity 4.3 Weakly compressible SPH method for solving fluid flow 4.3.1 Particle motion 4.3.2 Time integration 4.3.3 Time step criteria 4.4 Incompressible SPH method for solving fluid flow 4.4.1 Time integration 4.4.2 Discrete incompressible SPH algorithm 4.4.3 Time step criteria 4.5 Simulation of thermal fluid flow using ISPH 4.5.1 Semi-implicit time integration 4.5.2 Solution of the pressure Poisson equation 5 Verification of the SPH implementation 5.1 Transient heat conduction in laser-irradiated plate 5.1.1 Problem description 5.1.2 Dimensionless formulation 5.1.3 Numerical solution and results 5.2 Viscous flow 5.2.1 Couette flow 5.2.2 Poiseuille flow 5.3 Thermal convection 5.3.1 Natural convection in a square cavity 5.3.2 Rayleigh--Marangoni--Bénard convection in liquid aluminium 6 SPH model of direct laser interference patterning 6.1 Characteristics of the process 6.2 Thermal model 6.2.1 Non-dimensionalisation 6.2.2 Numerical solution of governing equation 6.2.3 Verification of the computation 6.2.4 Numerical test 6.3 Thermofluiddynamic model 6.3.1 Non-dimensionalisation 6.3.2 Numerical solution of governing equations 6.3.3 Discretisation 6.3.4 Resolution independence study 7 SPH simulation of direct laser interference patterning 7.1 Thermal model 7.1.1 DLIP experiments on stainless steel substrates 7.1.2 Thermal simulation of DLIP on steel substrate 7.2 Thermofluiddynamic model 7.2.1 Material properties and simulation parameters 7.2.2 Numerical results for steel substrate 7.2.3 Numerical results for aluminium substrate 7.2.4 Discussion and comparison with experiments 7.3 Extended thermofluiddynamic model 7.3.1 Model parameters 7.3.2 Influence of sulphur content on DLIP of stainless steel 8 Conclusions and outlook Bibliography

In this study, the wetting behavior of microstructured polyethylene terephthalate (PET) foils for polar and nonpolar liquids produced by plate-to-plate hot embossing is investigated. For the embossing step, stainless steel plates are used as stamps, which are microstructured with single-scaled and hierarchical textures using direct laser writing and two-beam direct laser interference patterning. The imprinted microstructures, containing pillar- and line-like textures, show increased water contact angles combined with a superoleophilic behavior. Time-resolved measurements reveal that oil droplets spread rapidly on the hierarchical textures with velocities of up to 1.4 mm2 s−1. This functionalization of PET foils creates new opportunities for a wide range of industrial applications, such as the use of oil-based instead of solvent-based paints, an improved distribution of lubricants in mechanical components or for oil–water separation in maritime surroundings.

Increasingly compact and powerful light emitting diodes require the development of efficient optical diffusers to manage their lighting capability according to the required application. In this study, a cost-effective strategy is demonstrated for fabricating micro-structured polymethylmethacrylate (PMMA) diffusers for white light sources. By combining different laserbased processes, namely direct laser engraving (DLE), direct laser writing (DLW), and direct laser interference patterning (DLIP), periodic patterns are fabricated in stainless steel surfaces with line- and dot-like geometries with feature sizes ranging from 1.7 to 900 μm. The fabricated hierarchical geometries are transferred to PMMA surfaces by plate-to-plate hot embossing. The relationship between the surface topography and the white light scattering behavior is investigated by confocal and scanning electron microscopy combined with photospectroscopy and image processing of photographs. The triple-scaled hierarchical structures can increase the haze up to 76% in the visible spectrum, while keeping the total transmittance over 90%, as the flat surface.

Laser patterning techniques have shown in the last decades to be capable of producing functional surfaces on a large variety of materials. A particular challenge for these techniques is the treatment of additively manufactured parts with high roughness levels. The presented study reports on the surface modification of additive-manufactured components of Ti64 and Al–Mg–Sc (Scalmalloy), with the aim of implementing water- and ice-repellent properties. Different laser-based microstructuring techniques, using nanosecond and picosecond pulses, are combined to create multiscale textures with feature sizes between ≈800 nm and 21 μm. The wettability could be set to static water contact angles between 141° and 153° for Ti64 and Al–Mg–Sc, respectively. In addition, surface free energy is analyzed for different surface conditions.

Advanced polymeric materials, such as polyether ether ketones (PEEK), have been placed as direct substitutes for metals and ceramics in diverse applications, such as the machinery industry and biomedical engineering. Moreover, surface treatments allow the emergence of brand-new properties or the improvement of preexisting ones, such as friction, lubrication, wettability, cellular infiltration, or osseointegration. A paramount approach to achieving topographical modifications is by using laser micro/nanoprocessing techniques such as direct laser interference patterning (DLIP). Herein, PEEK foils are structured with DLIP method using ultrashort pulses. The influence of the pulse duration between 266 fs and 15 ps and the pulse-to-pulse overlap on the resulting surface topography and chemistry is assessed. As a result, well-defined line-like textures with a period of 5.8 μm and aspect ratios up to 0.88 are achieved. Furthermore, it is possible to explore and understand the behavior of surface phenomena such as swelling, increase/decrease of laser–material interaction onset, and laser-induced periodic surface structures formation. A comprehensive topographical and chemical characterization study demonstrates that these distinctive topographical features occur because of multiphoton absorption, incubation effects, and heat accumulation. These phenomena allow structuring polymeric substrates that are low-absorbing and challenging to pattern with conventional nanosecond infrared (IR) laser sources.

Surface texturization of Transparent Conductive Oxides (TCOs) is a well-known strategy to enhance the light-trapping capabilities of thin-film solar cells and thus, to increase their power conversion efficiency. Herein, the surface modification of fluorine-doped tin oxide (FTO) using picosecond infrared direct laser interference patterning (DLIP) is presented. The surface characterization exhibits periodic microchannels, which act as diffraction gratings yielding an increase in the average diffuse transmittance up to 870% in the spectral range of 400–1000 nm. Despite the one dimensionality of the microstructures, the films did not acquire a significant anisotropic electrical behavior, but a partial deterioration of their conductivity is observed as a result of the removal of conductive material. This work proposes the feasibility of trading off a portion of the electrical conductivity to obtain a substantial improvement in the optical performance.