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Several beam shaping strategies have been proposed as an effective approach to fully exploit the average power delivered by the last generation of high power, industrial, femtosecond laser whilst avoiding unwanted thermal effects. Nevertheless, in the case of surface texturing, the effect of the profile modifications on the surface morphology has been barely investigated. The objective of our study is to understand more deeply how the beam profile features will impact the surface evolution. By tailoring the beam profile, we want to understand if it is possible to increase the process throughput. A comprehensive study has been carried out with a 35 W, 2MHz, femtosecond industrial laser. The impact of the beam intensity profile on texturing of metallic surface has been investigated. We systematically studied how the beam size (from 10 μm to few hundreds of microns) impacts the generation and evolution of Laser Induced Periodic Surface Structures (LIPSS) on Stainless Steel surface. SEM analysis has been carried out for all the generated morphologies.

Multi-Plane Light Conversion (MPLC) is an innovative shaping technique which allows theoretically lossless complex beam shapes. The free-space reflective design is particularly well suited to Ultra-Short Pulse (USP) laser-based processes challenges. We demonstrate the system high stability over long processing times thanks to a mode cleaning feature. Here we show micro-cutting and engraving tests carried out on stainless-steel and brass with a high power, industrial, USP laser having squared, and circular top-hat profile generated using MPLC technology. Thanks to the sharp edges of the profile, a sensible reduction of the taper and optimization of the overlapping is observed

Ultra-fast laser in micromachining have a reputation of highest precision and quality, which justifies additional invest in numerous applications. However, deficits in the synchronization of the positioning of beam deflection device and laser triggering -in particular at high repetition rates- still lead to defects like overtreatment due to the inertia of the mirrors of galvanometer scanners or path deviations at complex shapes. This in turn has led to an increasing demand of advanced pulse to pulse control for precise laser energy deposition. Two recent innovations have the potential to overcome these current limitations. Firstly, the scan ahead feature allows to calculate the actual beam position in acceleration and deceleration mode. According to the precise position feedback the control needs to adjust the repetition rate of the laser source e.g. at rectangular corners of a scan trajectory. Therefore, the pulse on demand feature at the laser interface is obligatory to dynamically adjust the pulse to pulse delay in order to accomplish constant energy deposition at any programmed scan pattern. We have put these two innovations to a test by combining an Excelliscan from Scanlab with an UV Tangor laser from Amplitude to validate the synchronization and constant pulse separation at various scan speeds and geometrical patterns. Applications trials like engraving with scan speed are presented in comparison to conventional scanning techniques to demonstrate the benefit of the fast synchronization and pulse on demand technologies.

Generation of nano or micro-scale structures on materials surface enables new functions and properties, such as super-hydrophobicity by lotus effect, surface blackening by light trapping, modification of surface tribological properties, etc. which are in high demand for a wide variety of industrial fields. Amongst the surface functionalization techniques, Ultra-Short Pulse lasers have been proven to be a reliable tool to create Laser Induced Periodic Surface Structures (LIPSS). Exploitation of LIPSS for industrial purposes poses some key problems like up scaling over large area with high repeatability and high throughput. Beam shaping could be a key element to overcome these issues. Specific shapes, such as top-hat line shape, could enable at once uniform processing over large surface with the consequence to reduce the processing time. Multi-Plane Light Conversion (MPLC) is an innovative technique of beam shaping which allows theoretically lossless complex beam shapes with a high control over amplitude and phase. The free-space reflective design allows for high beam shaping quality whilst maintaining the ultra-short property of the laser pulses, which is not usually achievable through other beam shaping methods. Here we show the results obtained over Stainless-Steel using an industrial femtosecond laser with a tophat line of 30μm × 594 μm intensity profile generated using MPLC technology. The beam has been delivered over the Stainless-Steel surface with a galvo scanner and focused through an f -theta lens of 100 mm. Surface morphology has been investigated via SEM and the processing time has been compared to conventional round Gaussian Beams

Femtosecond Laser Induced Surface Structures evolve from ripples to spikes upon the increase of the energy dose Φ. Nevertheless, for a fixed Φ, several process parameters (pulse energy, repetition rate, average power, overlapping, etc.) play an important role in determining the resulting morphology. Here we show that the beam intensity profile I as well has an important bearing on the structures morphology evolution. In the case of a Gaussian beam, I has been modified by varying the beam size d. We observed that for a stationary beam, and for a Φ value, passing from d = 13 µm to d = 200 µm makes possible the transition from ripples to spikes. This transition is made energetically advantageous by using a Top Hat profile. Compared to a 200 µm wide Gaussian beam, a 62 µm wide Top Hat reduces by 10 the Φ required to yield a similar surface morphology (coexistence of spikes and micro-groves). Confirming these results over a large surface could further validate the shaping of I as a key approach to both fully exploit the output power of state of the art, kW class, femtosecond laser whilst increasing the surface texturing throughput.

Laser-induced textures have been proven to be excellent solutions for modifying wetting, friction, biocompatibility, and optical properties of solids. The possibility to generate 2D-submicron morphologies by laser processing has been demonstrated recently. Employing double-pulse irradiation, it is possible to control the induced structures and to fabricate novel and more complex 2D-textures. Nevertheless, double-pulse irradiation often implies the use of sophisticated setups for modifying the pulse polarization and temporal profile. Here, we show the generation of homogeneous 2D-LIPSS (laser-induced periodic surface structures) over large areas utilizing a simple array of birefringent crystals. Linearly and circularly polarized pulses were applied, and the optimum process window was defined for both. The results are compared to previous studies, which include a delay line, and the reproducibility between the two techniques is validated. As a result of a systematic study of the process parameters, the obtained morphology was found to depend both on the interplay between fluence and inter-pulse delay, as well as on the number of incident pulses. The obtained structures were characterized via SEM (scanning electron microscopy) and atomic force microscopy. We believe that our results represent a novel approach to surface structuring, primed for introduction in an industrial environment.

Ultra-short pulse laser (UPL) industry is counting on high power P sources (100W class) to increase the throughput of a wide variety of industrial fabrication process. Nevertheless, this poses the challenge to overcome heat accumulation phenomena observed when P exceeds few tens of Watts compromising the machining quality. Novel beam engineering strategies are required to tackle this issue and guarantee high throughput with the high, distinctive, UPL machining quality. Here a study is reported on a variety of laser processes carried out with 100W class femtosecond lasers following two possible beam engineering strategies i.e. beam scanning with high speed (both a 100 m/s polygon scanner head and a 2D, 20 m/s fast, galvo-head) and parallel processing with multiple beams (obtained with both a DOE and an SLM head). Results show that by increasing P from few to 100 W also the throughput increases by nearly a factor 10 for micro-cutting (with galvo head and DOE) and even higher for surface texturing (with polygon scanner) while the machining quality is kept unchanged. Furthermore, we optimised the use of an SLM head for precise micro drilling of matrix holes showing the benefit of this technological approach in term of throughput. A full characterisation of the results carried out via optic and electronic microscopy will be also reported. We believe that all these results further increase the USP laser technology effectiveness level which is primed for industrial applications.

Controlling laser induced surface morphology is essential for developing specialized functional surfaces. This work presents novel, multi-scale periodic patterns with two-dimensional symmetry generated on stainless steel, polyimide and sapphire. The microstructures were realized by combining Direct Laser Interference Patterning with the generation of Laser Induced Periodic Surface Structures in a one-step process. An industrial, fiber femtosecond laser source emitting at 1030 nm with a pulse duration of 500 fs was utilized for the experiments. In the case of stainless steel, it was possible to create line-like or pillar-like surface patterns by rotating the polarization orientation with respect to the interference pattern. In the case of polyimide and sapphire, the absorption of the laser radiation was promoted by a multiphoton mechanism. In polyimide, grooves and pillars of several microns in depth were produced over an area much larger than the spot size. Finally, for sapphire, the simultaneous generation of interference-like pattern and laser induced periodic surface structures was realized. The results reported here provide valuable data on the feasibility to combine two state-of-the-art techniques with an industrial apparatus, to control the induced surface morphology.

Surface texturing by Ultra-Short Pulses Laser (UPL) for industrial applications passes through the use of both fast beam scanning systems and high repetition rate, high average power P, UPL. Nevertheless unwanted thermal effects are expected when P exceeds some tens of W. An interesting strategy for a reliable heat management would consists in texturing with a low fluence values (slightly higher than the ablation threshold) and utilising a Polygon Scanner Heads delivering laser pulses with unrepeated speed. Here we show for the first time that with relatively low fluence it is possible over stainless steel, to obtain surface texturing by utilising a 2 MHz femtosecond laser jointly with a polygonal scanner head in a relatively low fluence regime (0.11 J cm −2 ). Different surface textures (Ripples, micro grooves and spikes) can be obtained varying the scan speed from 90 m s −1 to 25 m s −1 . In particular, spikes formation process has been shown and optimised at 25 m s −1 and a full morphology characterization by SEM has been carried out. Reflectance measurements with integrating sphere are presented to compare reference surface with high scan rate textures. In the best case we show a black surface with reflectance value

The recent availability on the market of industrial, reliable, ultrashort pulse lasers (UPLs) delivering hundreds of watts has opened the possibility for this technology to significantly increase the machining throughput and address an ever-larger number of industrial applications. Nevertheless, heat accumulation phenomena are observed as soon as the average power P exceeds tens of watts, compromising the peculiar UPL machining quality. In this case, for a given machining process, it is determinant to implement a specific beam engineering strategy to mitigate thermal impacts, exploit the available P, and increase the throughput. Here, we show the results obtained in micro-cutting with an IR, femtosecond laser delivering Pmax = 100 W, at a maximum repetition rate of fmax = 10 MHz. The beam is first delivered through an innovative, fast, galvo scanner enabling a maximum speed of 20 m/s. A positive impact of high speed is observed for both the removal efficiency at high fluence and the machining quality at high power. In a second step, the beam is also split into three sub-beams enabling parallel processing. The authors show that, in this way, it is possible to fully exploit P, reduce the time taken by a factor of 10, and keep unchanged machining quality.

Micromachining with high repetition rate femtosecond lasers and galvo scanners shows some limitations in the pulses positioning accuracy due to the galvo mirrors acceleration. This is particularly evident during scan speed or direction changes, resulting in a poor quality and overtreatment e.g. in corners. Several scanning approaches have been proposed to tackle these issues like the so-called skywriting (SW) and the pulse-on-demand (POD) being the last limited to ns lasers, moderate pulse repetition rates and scan speeds. Recently, POD approach has been extended to femtosecond laser sources with high power and high repetition rate. Here, for the first time, we explored the huge potential in laser micromachining of femtosecond POD technology associated to a fast galvo scanner. We tested an innovative set-up allowing for precise laser triggering at the requested time and position for MHz repetition rate and scan speed as high as 20 m/s. The pulse position accuracy of the system has been estimated to be ≤ 1µm whilst performances have been evaluated in comparison to conventional scanning and SW. Finally, we report the results of an engraving test on stainless steel. The advantages of the approach we propose are clearly shown in terms of machining quality and precision with respect to conventional scanning and reduction of the processing time by ≈ 40% with respect to SW.

Laser surface texturing is an established way to introduce surface functionalities on solid surfaces. By means of femtosecond laser sources, it’s possible to texture a variety of solids such as metals, semiconductors and transparent materials, introducing features of different symmetry and size. Fabrication of laser induced periodic surface structure (LIPSS) which typically range in the near-submicron length scale can lead to strong modifications of surface wetting, tribological and optical properties. Controlling LIPSS morphology could enable us to mimic functional textures found in nature, introducing functionalities such as antireflectivity and bactericidity. Several works demonstrate the impact of polarization control and double-pulse irradiation on determining texture symmetry and size. Here we present a comprehensive study on controlling laser induced structures by double femtosecond pulse irradiation. The effect of pulse polarization and interpulse delay is elucidated and the generation of novel 2D surface morphologies is reported. A plausible interpretation of the structure formation mechanism is proposed in the frame of non-linear convection flow. A high average power industrial femtosecond laser source with a pulse duration of 350 fs operating at high repetition rate was employed for the experiments. Large areas were processed by combining different 2D morphologies generating a holographic pattern. We believe that our results provide a novel insight in controlling laser induced submicron morphology. Moreover, the presented surface texturing process is scalable in terms of processed area and cycle time and fully compatible with high repetition rates, demonstrating for the first time the feasibility to introduce double-pulse processing in an industrial environment.

Femtosecond lasers have been proved to be an effective fabrication tool to process with high machining quality and negligible thermal effects a wide variety of materials. However, the system technology enabling fast and precise scanning on the workpiece, currently limits the average power of these laser sources to less than 10 Watts of average power in most industrial application. To overcome this limitation, a proportional up-scaling of both, the laser repetition rate and scan speed is needed, demanding for faster scanning technologies. Recently, rugged, femtosecond lasers delivering pulses with repetition rates of several MHz and pulse energy up to some hundreds of μJ have been introduced to the market. In parallel, the development and commercialization of novel galvanometric scanner heads, enabling scan speeds well above 10 m/s is ongoing. Here we explored the capabilities of a novel set-up consisting of an industrial femtosecond laser delivering 100 W with a repetition rate up to 13 MHz coupled with an innovative galvanometric scanner head enabling scan speeds up to 30 m·s-1. On stainless steel, we carried out engraving tests with both single line grooving and multiple surface raster scanning. By systematic variation of repetition rate and pules overlap we investigate how the machining quality and the ablation rate depend on the average laser power at different fluence levels. Heat accumulation effects are evaluated via Scanning Electron Microscope. Finally, we show how to scale-up the cutting of a 500 μm thick stainless-steel part varying the scan speed from 1 m·s-1 to 20 m·s-1.

We present a systematic study on the generation of 2D surface structures on stainless steel, using double, crosspolarized femtosecond pulses with variable interpulse delay. We demonstrate the combined effect of the interpulse delay and key process parameters in order to obtain periodic structures. The sets of double pulses were produced utilizing a modified Michelson interferometer with interpulse delay varying from -100 ps to +2 ns. The study was carried out with an industrial laser having pulse duration of 350 fs, emitting in the near infrared (λ = 1030 nm), operating at 100 kHz coupled with a Galvo scanner. We evaluate the obtained surface morphology and structure period using SEM characterization and Fourier analysis.

Nowadays the relevance and the robustness of ultrafast lasers are well established for many industrial applications. Indeed this laser technology combines the unique capacity to process any type of material with an outstanding processing precision and a minimal heat affected zone. The key issue is to combine high throughput, low residual thermal load and good processing quality. Thanks to high average power and high repetition rate it is possible to achieve high throughput providing that the operating parameters are precisely tuned to the application, otherwise heat accumulation and heat affected zone may appear, leading to detrimental effects such as burr, uncontrolled melting and metal oxidation. In this paper we report on high-throughput laser ablation of metals using a 100W- and 10MHz- ultrafast laser. Target materials were stainless steel, Copper, and Aluminum. Operating parameters such as fluence, repetition rate and scanning velocity have been considered. Results are discussed in terms of ablation efficiency, surface morphology, multipass and upscaling capabilities. Different behaviors between materials are also discussed. We observe that pulse-to-pulse pitch and delay are key parameters that must be taken into account in order to define relevant process windows for each material. The use of polygon scanner instead of galvo scanner enables us to reduce the thermal load along the laser trajectory. The point is not to avoid heat accumulation but to take advantage of this phenomenon as long as the target material can stand the thermal load without detrimental effects on the processing quality.

Surface structuring by femtosecond lasers has emerged as an efficient tool to functionalize the surfaces of various solid materials. Laser induced periodic surface structures (LIPSS) can drastically impact the wetting, friction and optical properties of the surface depending on the size, aspect ratio and period of the structures. Morphological characteristics in the nanoscale, such as nano roughness, contributing to a hierarchical surface formation are considered to have a significant impact on those properties. In this study, we demonstrate for the first time to our knowledge the feasibility of inducing ripples and spikes utilizing a 257 nm femtosecond laser. LIPSS with a period smaller than 200 nm were realised. Furthermore, we show the evolution of those structures into conical spikes for this wavelength, and we provide an interpretation on their formation. Finally, we show that sub 200 nm LIPSS can create subwavelength gratings providing non-angular dependent light reflection and non-periodic morphologies showing super hydrophobic behaviour.

Surface functionalization is a rapidly growing application for industrial ultrafast lasers. There is an increasing interest for high throughput surface processing, especially for texturing and engraving large manufacturing tools for different industrial fields such as injection molding, embossing and printing. Hydrophobic and hydrophilic surfaces, colored or deep black metal surfaces can now be industrially produced. The engraving speed is continuously improving following improvements in beam scanning technology and high average power industrial ultrafast lasers. Several tenths of MHz for the laser repetition rate and several hundreds of meter per second for the beam speed are available. More than 100 m/s scanning speed is then possible for laser surface structuring. But these surfaces are quite hard to produce since it is necessary to have a good compromise between high removal rate and high surface quality (low roughness, burr-free, narrow heat affected zone). In this work, we apply a simple engineering model based on the two temperature description of ultra-fast ablation to estimate key processing parameters. In particular, the pulse-to-pulse overlap which depends on the scanning velocity, the spot size, and the laser repetition rate all have to be adjusted to optimize the depth and roughness, otherwise heat accumulation and heat affected zone may appear. Optimal sequences of time and spatial superposition of pulses are determined and applied with a polygonal scanner. Ablation depth and processing speed obtained are compared with experimental results.

Over the past few years, dye-sensitized solar cell (DSC) research has been focused on the material and process cost reduction, and on the electronics integration of the devices. Monolithic design is one of the most promising DSC architectures for mass production, because it allows the elimination of one conductive substrate and offers the possibility of printing layer-by-layer the materials that compose the structure. In this study, the formulation, the realization, and the processing of the spacer and the catalyst layers are proposed, and the relative performance in terms of J-V characteristics, incident photon to current conversion efficiency, and impedance analysis of the device with the optimized material thickness is reported. The optimized profile of the overall structure permits us to obtain masked cells with a conversion efficiency of about 5% with no chemical treatment.

The combination of both, fast beam scanning systems and high repetition rate, high average power lasers, represents an interesting technological solution for surface texturing by Ultra-Short Pulses Laser to gain a foothold into industrial environment for commercial purposes. Nevertheless unwanted thermal effects are expected when the average power exceeds some tens of W. An interesting strategy for a reliable heat management would consists of texturing surfaces with a low fluence values (slightly higher than the ablation threshold) and utilising a polygon scanning head which is able to deflect the laser beam with unprecedented speed. Here we show that over stainless steel, it is possible to obtain different surface textures (in particular ripples, micro grooves and spikes) by utilising a 2 MHz femtosecond laser jointly with a fast and accurate polygonal scanner head at relatively low fluence (0.11 J·cm -2 ). The evolution of the Laser induced surface structures morphology is shown when varying the scan speed between 25 m·s -1 and 90 m·s -1 . Two different wavelengths have been utilised for the process λ= 1030 nm and λ = 515 nm and the difference of the results obtained have been highlighted. Moreover, a full structures morphology characterization by SEM has been carried out for all the textured surfaces. Finally, by increasing the number of successive surface scans is possible to tailor the surface reflectivity. As a result an average reflectivity value of < 5% over the visible range has been extracted from a blackened stainless steel surface.

We have analysed and optimised a laser process for the sintering of the TiO2 layers in dye solar cells (DSCs). Through a thermographic characterisation of the process, we show that it is possible to scale and process large areas uniformly (16 cm2). We fabricated DSCs with nanocrystalline (nc)-TiO2 films sintered by using pulsed ultraviolet laser with an average output power P varying from 1 W to 7 W whilst mainting a constant power conversion efficiency η. The highest efficiency reached for a laser sintered DSC was 7%. The time required to sinter 1 m2 of nc-TiO2 film was found to decrease hyperbolically with P, which is important for determining process takt times. We quantified the embodied energy (EE) required to sinter 1 m2 of the active TiO2 layer for a variety of different processes, and found that the EE for the laser sintering process with a system wall plug efficiency of 3.5% to be competitive with the more conventional oven and belt furnace treatments. We outline the main features required from a laser system to carry out an efficient, energetically favourable and industrially applicable automated process with competitive throughput. Copyright © 2012 John Wiley & Sons, Ltd.

Deep engraving of 3D textures is a very demanding process for the creation of master tool e. g molds, forming tools or coining dies. As these masters are uses for reproduction of 3D patterns the materials for the tools are typically hard and brittle and thus difficult to machine. The new generation of industrial femtosecond lasers provides both high accuracy engraving results and high ablation rates at the same time. Operation at pulse energies of typically 40 μJ and repetition rates in the Mhz range the detrimental effect of heat accumulation has to be avoided. Therefore high scanning speeds are required to reduce the pulse overlap below 90%. As a consequence scan speeds in the range of 25-50 m/s a needed, which is beyond the capability of galvo scanners. In this paper we present results using a combination of a polygon scanner with a high average power femtosecond laser and compare this to results with conventional scanners. The effects of pulse energy and scan speed of the head on geometrical accuracy are discussed. The quality of the obtained structures is analyzed by means of 3D surface metrology microscope as well as SEM images.

In this work we exploit the use of a new promising class of light harvesting materials, namely the hybrid organic halide perovskites (CH 3 NH 3 PbI 3-x Cl x ), for the fabrication of mesoscopic perovskite solar cells and series-connected monolithic perovskite module. To achieve this goal, important innovative procedures were implemented in order to define a reproducible fabrication path applicable also to large area devices. Small area solar cells were fabricated with both Spiro-OMeTAD and the P3HT polymer as Hole Transporting Material (HTM) both showing a Power Conversion Efficiency (PCE) up to 10.5%. First attempts to scale up the size of the cell to a module size shown a PCE of 5.1% on an active area of 13.44cm2. In order to improve the efficiency of the module, we developed a new Laser assisted patterning of the perovskite/compact layers together with an optimized perovskite deposition in controlled atmosphere. This allowed us to improve the module PCE up to 7.3% which represent the state of art efficiency for a perovskite module. A promising long-term stability was obtained for the module with Spiro-OMeTAD as HTM. Supporting simulations of Mesoscopic Perovskite Solar Cells were obtained by using the multiscale device simulator TiberCAD.

Here for the first time an high power, high repetition rate, ultra short pulses, Yb doped fiber laser has been used jointly with a trepanning head to carry out hole trepanning trials in 900 µm thick stainless steel L316. Holes with aspect ratio up to 24 have been shown. Holes geometry has been characterized showing a profile which is cylindrical. The trepanning time has been optimized and reduced to 1.5 s. These results show not only the huge potential introduced in material hole trepanning by coupling high power, high repetition rate, fs laser with an innovative trepanning head but also pave the way for the application of laser trepanning in future fields such as automotive and microelectronics.Here for the first time an high power, high repetition rate, ultra short pulses, Yb doped fiber laser has been used jointly with a trepanning head to carry out hole trepanning trials in 900 µm thick stainless steel L316. Holes with aspect ratio up to 24 have been shown. Holes geometry has been characterized showing a profile which is cylindrical. The trepanning time has been optimized and reduced to 1.5 s. These results show not only the huge potential introduced in material hole trepanning by coupling high power, high repetition rate, fs laser with an innovative trepanning head but also pave the way for the application of laser trepanning in future fields such as automotive and microelectronics.

Flexible Dye Solar Cells (FDSCs), in their most widespread architecture, are assembled with two opposing planar films or foil substrates in metal–plastic or plastic–plastic combinations. The use of one metal electrode enables the convenient utilization of materials and high temperature processes but is accompanied by issues including partial opacity of the electrolyte and catalyst layer. Constraints on the stability of plastic substrates have led to the development of a variety of alternative material formulations and processes to guarantee performance even at low temperatures compatible with plastic films. Recently, efforts in doing without transparent conducting oxides have led to the development of new unconventional architectures. Review of the operation of DSCs shows that initial target markets are represented by indoor applications where power output densities have been shown to outperform competing flexible photovoltaic technologies. Whereas performance, stability in particular, needs to be significantly improved for the adoption in long term outdoor installations, commercial products integrating FDCSs for indoor or portable use have already been launched. Issues pertaining progress in materials, processes, devices and industrialization of FDSCs will be analyzed and discussed in this review.

A crucial step in Dye Solar Cell (DSC) fabrication is the sintering of the TiO2 layer which needs to guarantee good electromechanical bonding between nanoparticles whilst maintaining sufficiently large porosity to yield performing devices. The standard procedure for TiO2 sintering requires firing in an oven at ∼ 500°C. An alternative procedure consists in utilizing laser scanning processing which has the advantageous potential of being noncontact, local, low cost, rapid, selective, automated and scalable. We analyzed and optimised a laser process for the sintering of the TiO2 layers in dye solar cells analyzing temperature profiles, throughput and the embodied energy. The development of electronic and photovoltaic devices on plastic substrates is of considerable interest due to the advantages they bring in terms of flexibility and easy processing for lightweight, low-cost large-area applications. An alternative sintering procedure compatible with flexible substrates and large area processing consists in utilizing a UV lamp. We subjected TiO2 pastes deposited on conductive transparent substrates to UV irradiation. Fully plastic devices fabricated through this method showed efficiencies of 4%.

We have carried out a systematic and combined I- V, electrochemical impedance spectroscopy (EIS), and scanning emission microscopy (SEM) investigation of dye solar cells (DSCs) fabricated with laser-sintered TiO2 photoanodes as a function of laser-integrated fluence Φ. We show that the electron lifetime τoc in the TiO2 film extracted from EIS spectra monotonically increases with laser sintering fluence both at constant illumination and, even more significantly, at constant photoinduced charge Qoc. The increase in τoc between the poorly sintered and the best laser-sintered devices is an order of magnitude at constant illumination (equivalent to the increase in device efficiency) and even greater at constant Qoc. A strong correlation between τoc and the cell electrical parameters is observed, although device efficiency peaks with Φ whereas τoc does not. The rise of τoc with Φ indicates improved electromechanical bonding between TiO2 nanoparticles due to the improved sintering carried out by the raster scanning laser process, as also confirmed by SEM images. The strong correlation between device performance and τoc indicates that laser processing may also have significant potential in many other device applications that require high-surface-area TiO2 coupled with good electronic transduction.

Scanning laser processing has become a useful and often used tool in thin film solar cell industries, since it enables precise, low cost, non-contact and highly automated fabrication processes such as scribing, patterning, marking, edge deletion, local melting and sintering. Dye Solar Cells (DSCs) are electrochemical photovoltaic devices representing an attractive technology for large area solar energy conversion since they utilize relatively cheap materials and simple manufacturing processes often “borrowed” from the printing industry. In this paper we show successful application of laser processing to this technology.

Making use of an interferometric diagnostic system, we analyze the thermo-mechanical distortions taking place in the slab shaped ceramic Nd:YAG active medium of a 100 W class laser. These distortions are collected in different pumping regimes, both in static situations and during transient warm-up, and compared to the results of computer simulations. This procedure enables us to determine the relevance of different stress causes and thus to increase the specific power extraction of the active slab module.

Nowadays, the relevance of ultrashort laser is well established for many medical or industrial applications. Indeed, the ultrashort laser technology has reached a high level of robustness which makes it compatible with the needs of industry. This laser technology combines the unique capacity to process any type of material with an outstanding precision and a minimal heat affected zone. Thanks to high average power and high repetition rate it is possible to achieve high throughput providing that the operating parameters are finely tuned to the application, otherwise heat accumulation and heat affected zone may appear. In this paper, the authors report on high throughput single pass ablation of stainless steel with a high average power Yb-doped fiber ultrashort pulse laser which is tunable in pulse duration from 350 fs to 10 ps and in repetition rate from 200 kHz to 2 MHz. The influence of pulse duration, repetition rate, fluence, energy dose, and scanning velocity will be discussed in terms of ablation eff...

Novel approaches for the fabrication of dye-sensitized solar cells (DSCs) are reported in which all the main constituent materials are processed by laser radiation. In addition to laser sintering of the nanocrystalline TiO2 film it is shown that lasers can be successfully utilized for nc-TiO2 film patterning, platinization of the counter-electrode, and efficient gasket sealing. All the mentioned processes are optimized and utilized for the fabrication of the first efficient and durable all-laser-based DSCs. Under one sun A.M. 1.5 illumination the power conversion efficiency (PCE) is 5.3% (6.2% unmasked) and also greater than or equal to the PCE of the cell fabricated with the same materials set but processed using conventional procedures (5.2%). These results open up a new scenario for DSC technology, i.e., that of setting up an entire, laser-based, three-step DSC pilot production line with tangible advantages in terms of effective processing, automation, large area scalability, and embedded energy.

By identifying the right combination of laser parameters, in particular the integrated laser fluence Φ, we fabricated dye solar cells (DSCs) with UV laser-sintered TiO2 films exhibiting a power conversion efficiency η=5.2%, the highest reported for laser-sintered devices. η is dramatically affected by Φ and a clear trend is reported. Significantly, DSCs fabricated by raster scanning the laser beam to sinter the TiO2 films are made as efficient as those with oven-sintered ones. These results, confirmed on three batches of cells, demonstrate the remarkable potential (noncontact, local, low cost, rapid, selective, and scalable) of scanning laser processing applied to DSC technology.

Ultra-short pulse (USP) Laser Induced Periodic Surface Structures (LIPSS) namely ripples, micro-grooves and spikes [1] have received considerable attention since they can modify some key surface properties like wettability, colour and tribology, increasing the material's internal value [2]. Nevertheless, the complete understanding of the physical mechanisms leading to LIPSS formation is still under debate. Even so, at repetition rate values as high as several kHz, the fluence Φ and the overall energy irradiated over a unit surface (dose) have been identified as the physical parameters playing a major role in the structures generation process [3][4][5].