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Imaging Capability of Terahertz and Millimeter-Wave Instrumentations for NDT of Polymer Materials
(2006)
The paper presents numerical methods to detect and classify defects and inhomogeneities by means of active thermography. The objective is to determine the wall thickness of structure elements with an inaccessible back wall, for example, of pipes or Containers. As test specimens we used approximately 2 cm thick PVC samples with spatial variations in the back wall geometry. Flash lamps provided the heating. To know the thickness of the wall, we used two inversion methods and compared the results achieved. One is an iterative echo defect shape method and already tested on Steel test specimens with good reconstruction results. The second one is the Levenberg-Marquardt method, applied here to thermographic data for non-destructive testing. Since data capturing using active thermography and the presented numerical methods can easily be automated, the combination of these two procedures is a promising approach providing a broad area of application.
Structuring of thin-film photovoltaic modules requires basic knowledge of the laser – thin-film interaction in order to adapt the accessible laser parameters, like wavelength, power, repetition rate and scribing speed whilst taking into account the specific material properties of the layer. We have studied the nanosecond laserablation behavior of corresponding layers (i) of silicon based thin-film solar cells with a-Si/µc-Si tandem absorber type and (ii) of back contact and absorber layer of CIGSe solar cells. The respective ablation threshold fluences were determined as integrative parameters describing the specific laser – material interaction. For the threshold determination we used two different methods and developed a new analytical approach taking into account scribing through the glass substrate as it is preferred for most structuring processes. This was done by analyzing the thin film ablation results by means of optical microscopy, profilometry, scanning electron microscopy (SEM). Moreover, we determined the incubation coefficient of the regarded material layers which allows us to predict quantitatively the influence of the spot overlap on the scribing threshold.
Manufacturing of CIGSe thin film solar modules involves typically one laser structuring step (P1) and two mechanical structuring steps (P2 and P3) for serial interconnection. In our approach, complete laser structuring is successfully demonstrated by application of short nanosecond laser pulses (<10 ns) with a single, visible wavelength of 532 nm. The P1 and the P3 trenches are scribed by induced and direct ablation, respectively. For the P2 scribe, the thermal input of the ns laser pulses is used to transform the CIGSe absorber layer locally into a highly conductive compound to provide proper electrical interconnection. These findings promise further simplification and flexibility to thin film solar cell production.
Ein wesentlicher Vorteil der Dünnschichtphotovoltaik gegenüber der waferbasierten Photovoltaik liegt in der monolithischen Serienverschaltung. Bei der Herstellung von Chalkopyrit(CIGSe) -Dünnschicht-Solarmodulen erfolgen dafür typischerweise ein Laser-Strukturierungsschritt (P1) und zwei mechanische Strukturierungsschritte (P2, P3). In diesem Beitrag wird gezeigt, dass die Strukturierung von CIGSe-Solarmodulen vollständig mit kurzen Laserpulsen (<10 ns Pulsdauer) und einer einzigen Wellenlänge (532 nm) möglich ist. Der P1- und P3-Schnitt erfolgen durch direkte induzierte Ablation. Für den P2-Schnitt wird gezielt der hohe Wärmeeintrag der ns-Laserpulse genutzt, um die CIGSe-
Absorberschicht lokal aufzuschmelzen und strukturell so zu verändern, dass eine elektrisch gut leitende Verbindung zwischen Front- und Rückkontakt entsteht.
One wavelength fits all
(2011)
Structuring of Thin-film Solar Cells with a Single Laser Wavelength Structuring of a PV module into a number of cells is necessary to lower the current and to increase the voltage, and is typically accomplished with nanosecond laser pulses of different wavelengths. Duetothe many available laser sources, complex and expensive scribing Setups are necessary. To overcome this a concept for laser structuring of thin-film PV modules using a single wavelength allows prediction ofthe ablation behaviourfor a given laser pulse energy.