The thin-film solar cell market has seen a period of consolidation during the last years and many involved companies
were forced to stop production due to increasing price pressure from competing cell technologies. Today, thin-film solar
industry is gaining momentum again. Especially Cu(In,Ga)Se2 technology evolves at high pace fired by recently achieved
record efficiencies of 20.4 percent on flexible polyimide substrate [1] and 20.8 percent on glass substrate [2]. Fresh
companies are preparing market entry with matured products and manufacturing technology suitable for high-volume
and high-throughput production. Among these key-enabling technologies is laser patterning for cell-to-cell
interconnects. Several research groups worked on efficient and reliable laser processes that are now ready for the
industrial assessment. Here we present a set of work-horse processes for P1, P2 and P3 scribing of CIGS cells on glass
substrate. Optimized parameters are presented for 532 nm and 1064 nm using 50 ps pulses from an all-in-fiber laser
system. We further demonstrate the successful realization of functional 8-cell modules with a reduced “dead-zone”
width of 70±5 μm and high efficiencies. The certified efficiency of 16.6 percent for our low-dead-zone champion module
confirms the observation that shrinking of interconnects has no adverse effects on their electrical quality.
New developments in the thin film solar market continue the trend towards solar modules with higher energy conversion while at the same time, reducing significantly manufacturing costs. Especially thin film technologies based on Cadmiumtellurid (CdTe) or Cu(In,Ga)(S,Se)2 (CIGS) seem to be suited to improve the energy conversion and hence, take over larger market shares. With this work, we present our latest achievements towards a CIGS all laser scribing process with the emphasis on structuring the absorber layer and its implications to the production. While P1 laser scribing through the substrate is already implemented in production today a variety of different approaches, like lift-off, ablation, or remelting are possible for the P2 process where commonly a mechanical process is state of the art. One challenge which the P2 and P3 processes face is the layer side processing. Therefore a thorough investigation has been conducted including different laser wavelengths (355 nm to 1550 nm), pulse durations (10 ps to 100 ns), and beam shaping to find the best possible solution for each scribing process. Optimization took place utilizing not only resistance measurement and optical microscopy but also LSM, REM, EDX, EL, and Lock-In Thermography. Combining the best results of each scribing process and using a high speed, high accuracy motion system a functional lab size module has been produced with a reduced dead zone of below 200 m. In an outlook, a way is presented on how to take the lab results into a productive system and place it in a manufacturing environment.
Recent developments in Cu(In,Ga)Se2 (CIGS) thin film photovoltaics enabled the manufacturers to produce highly
efficient solar modules. Nevertheless, the production process still lacks a competitive process for module patterning.
Today, the industry standard for the serial interconnection of cells is still based on mechanical scribing for the P2 and
P3 process. A reduction of the non-productive "dead zone" between the P1 and P3 scribes is crucial for further
increasing module efficiency. Compact and affordable picosecond pulsed laser sources are promising tools towards all-laser
scribing of CIGS solar modules. We conducted an extensive parameter study comprising picosecond laser sources
from 355 to 1064 nm wavelength and 10 to 50 ps pulse duration. Scribing results were analyzed by laser scanning
microscope, scanning electron microscope and energy dispersive X-ray spectroscopy. We developed stable and reliable
processes for the P1, P2 and P3 scribe. The best parameter sets were then used for the production of functional mini-modules.
For comparison, the same was done for a selection of nanosecond pulsed lasers. Standardized analysis of the
modules has shown superior electrical performance of the interconnections and confirmed the feasibility of a dead zone
width of less than 200 ìm on an entire mini module.
The solar photovoltaic market is continuously growing utilizing boths crystalline silicon (c-Si) as well as thin film
technologies. This growth is directly dependant on the manufacturing costs for solar cells. Factors for cost reduction are
innovative ideas for an optimization of precision and throughput. Lasers are excellent tools to provide highly efficient
processes with impressive accuracy. They need to be used in combination with fast and precise motion systems for a
maximum gain in the manufacturing process, yielding best cost of ownership.
In this article such an innovative solution is presented for laser scribing in thin film Si modules. A combination of a new
glass substrate holding system combined with a fast and precise motion system is the foundation for a cost effective
scribing machine. In addition, the advantages of fiber lasers in beam delivery and beam quality guarantee not only
shorter setup and down times but also high resolution and reproducibility for the scribing processes P1, P2 and P3. The
precision of the whole system allows to reduce the dead zone to a minimum and therefore to improve the efficiency of
the modules.
Drilling holes with pulsed Nd:YAG lasers is well researched and state-of-the-art within a variety of industrial applications. Surgical needles in the medical field, turbine blades for the aviation industry, and gas filter for the automotive industry are just some examples that come to mind. Similar to other industrial developments over the last century this market asks for higher throughput, smaller diameter, higher aspect ratios, and of course within a minimum of tolerances. New laser sources and specially developed processes are entering the market to move the mere drilling to the next level of micro drilling. It is crucial to understand the application and the influence of the process parameters to develop a suitable, stable, and repeatable work process. Commonly used pulses within the microsecond-regime show a significant thermal side effect which is unacceptable if used e.g. in combustion nozzles. Reducing the thermal load by shortening the pulse length into the nanosecond-regime could be a compromise to bridge the gap between quality and production speed in high precision laser drilling. However, depending on the relation between pulse energy, pulse repetition rate, and "helical speed" a reduced, but existent, thermal effect is inevitable. The scope of this paper is to show the influences of the process parameters in helical drilling with a new developed nanosecond pulsed Nd:YAG laser at its fundamental wavelength of 1064 nm. A variation of drilling-optic principles in different materials are studied and the advantages as much as the disadvantages are discussed.
Micro-joining and hermetic sealing of dissimilar and biocompatible materials is a critical issue for a broad spectrum of products such as micro-electronics, micro-optical and biomedical products and devices. Today, biocompatible titanium is widely applied as a material for orthopedic implants as well as for the encapsulation of implantable devices such as pacemakers, defibrillators, and neural stimulator devices. Laser joining is the process of choice to hermetically seal such devices.
Laser joining is a contact-free process, therefore minimizing mechanical load on the parts to be joined and the controlled heat input decreases the potential for thermal damage to the highly sensitive components. Laser joining also offers flexibility, shorter processing time and higher quality. However, novel biomedical products, in particular implantable microsystems currently under development, pose new challenges to the assembly and packaging process based on the higher level of integration, the small size of the device's features, and the type of materials and material combinations. In addition to metals, devices will also include glass, ceramic and polymers as biocompatible building materials that must be reliably joined in similar and dissimilar combinations. Since adhesives often lack long-term stability or do not meet biocompatibility requirements, new joining techniques are needed to address these joining challenges. Localized laser joining provides promising developments in this area. This paper describes the latest achievements in micro-joining of metallic and non-metallic materials with laser radiation. The focus is on material combinations of metal-polymer, polymer-glass, metal-glass and metal-ceramic using CO2, Nd:YAG and diode laser radiation. The potential for applications in the biomedical sector will be demonstrated.
Implantable microsystems currently under development have the potential to significantly impact the future treatment of disease. Functions of such implants will include localized sensing of temperature and pressure, electrical stimulation of neural tissue and the delivery of drugs. The devices are designed to be long-term implants that are remotely powered and controlled for many applications. The development of new, biocompatible materials and manufacturing processes that ensure long-lasting functionality and reliability are critical challenges. Important factors in the assembly of such systems are the small size of the features, the heat sensitivity of integrated electronics and media, the precision alignment required to hold small tolerances, and the type of materials and material combinations to be hermetically sealed. Laser micromachining has emerged as a compelling solution to address these manufacturing challenges. This paper will describe the latest achievements in microjoining of metallic and non-metallic materials. The focus is on glass, metal and polymers that have been joined using CO2, Nd:YAG and diode lasers. Results in joining similar and dissimilar materials in different joint configurations are presented, as well as requirements for sample preparation and fixturing. The potential for applications in the biomedical sector will be demonstrated.
Advanced microsystems for optoelectronic and biomedical applications incorporate a variety of non-metallic materials such as glass, silicon, sapphire and polymers. Examples include switches and multiplexers for fiber-optical data transmission in telecommunications, and innovative implantable microsystems currently being developed to monitor, stimulate and deliver drugs. Laser micromachining has proven to be an effective tool to address specific manufacturing challenges for these devices. Investigations have been conducted on laser ablation for precise localized material removal, laser cutting, and drilling; and application data for a range of relevant materials already exists. In contrast, applications of laser joining are currently limited to microwelding and soldering of metals. The assembly of SMD’s and the sealing of pacemakers are typical examples.
This paper will describe the latest achievements in laser microjoining of dissimilar materials. The focus will be on glass, metal and polymer that have been joined using CO2, Nd:YAG and diode lasers. Results in joining similar and dissimilar materials in different joint configurations will be presented, as well as requirements for sample preparation and fixturing. The potential for applications in the optoelectronic and biomedical sector will be demonstrated.
New joining techniques are required for the variety of materials used in the manufacture of microsystems. Lasers are emerging as a useful tool for joining miniaturized devices. The beam can be focused to less than .001 inch allowing localized joining of very small geometries. There is minimal heat input into the part so distortion and change in material properties is minimal. The high quality of the laser welds and the precise process control enable hermetic sealing.
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