Laser scribing is an indispensable step in the industrial production of Cu(In,Ga)Se2 thin film solar modules. While cell separation (P1 and P3) is usually achieved using high velocity, low overlap lift-off processes, removal of the absorber layer for generating an electrical back-to-front interconnect (P2) is typically a slow process. In the present study we present an approach for scaling the classical P2 process velocity to an industrially exploitable level. We demonstrated successful P2 scribing at up to 1.7 m/s in a single beam, single pass configuration using a linear focal spot. The presented process is robust against variations in the scribing velocity and focal position, a key point for successful machine integration.
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.
Here, we demonstrate all-fiber direct amplification of 11 picosecond pulses from a gain-switched laser diode
at 1063 nm. The diode was driven at a repetition rate of 40 MHz and delivered 13 μW of fiber-coupled
average output power. For the low output pulse energy of 0.33 pJ we have designed a multi-stage core
pumped preamplifier based on single clad Yb-doped fibers in order to keep the contribution of undesired
amplified spontaneous emission as low as possible and to minimize temporal and spectral broadening. After
the preamplifier we reduced the 40 MHz repetition rate to 1 MHz using a fiber coupled pulse-picker. The final
amplification was done with a cladding pumped Yb-doped large mode area fiber and a subsequent Yb-doped
rod-type fiber. With our setup we achieved amplification of 72 dBs to an output pulse energy of 5.7 μJ, pulse
duration of 11 ps and peak power of >0.6 MW.
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