Flexible large area organic photovoltaic (OPV) is currently one of the fastest developing areas of organic electronics.
New light absorbing polymer blends combined with new transparent conductive materials provide higher power
conversion efficiencies while new and improved production methods are developed to achieve higher throughput at
reduced cost. A typical OPV is formed by TCO layers as the transparent front contact and polymers as active layer as
well as interface layer between active layer and front contact. The several materials have to be patterned in order to allow
for a row connection of the solar cell. 3D-Micromac used ultra-short pulsed lasers to evaluate the applicability of various
wavelengths for the selective ablation of the indium tin oxide (ITO) layer and the selective ablation of the bulk hetero
junction (BHJ) consisting of poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) on top of a
Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) without damaging the ITO. These lasers in
combination with high performance galvanometer scanning systems achieve superior scribing quality without damaging
the substrate. With scribing speeds of 10 m/s and up it is possible to integrate this technology into a roll-to-roll
manufacturing tool. The functionality of an OPV usually also requires an annealing step, especially when using a BHJ
for the active layer consisting of P3HT:PCBM, to optimize the layers structure and therewith the efficiency of the solar
cell (typically by thermal treatment, e.g. oven). The process of laser annealing was investigated using a short-pulsed laser
with a wavelength close to the absorption maximum of the BHJ.
As advancements thin-film and flexible electronics like printed organic solar cells and organic LEDs bring these devices
close to market entry new processing technologies for cost-effective, high quality production have to be developed. Laser
technology provides a huge potential to fulfill the demanding tasks that come with the transition from lab to factory.
3D-Micromac looked into the possibilities of ultra-short pulsed lasers for scribing of transparent conductive layers as
well as active layers of organic solar cells. This paper presents the results of this research.
Presently, there is a growing demand from the industry for microprocessing of materials. For applications in microsystems technology and biotechnology it is particularly necessary to produce structures with dimensions down to the micrometer scale. This refers especially to materials that can not or not in a sufficiently quality be processed by conventional methods of silicon technologies.
In order to fulfil the industrial demands we have investigated the structuring of anodic bondable PYREX glass and of polymers by means of laser microprocessing using the excimer laser mask projection technique (193 nm wavelength, 10 ns pulse duration, 8 mJ pulse energy, 500 Hz repetition rate). In our paper we will show the dependence of the obtained quality especially the roughness of the generated surfaces on the processing parameters. The possibilities of our technology including the creation of holes, channels and three dimensional microstructures will be presented too. Single structures e.g. bridges and grooves are attainable with widths of 10 micrometers and below. Some of the drilled holes (diameter about 50 µm) have been successfully filled inside with aluminium by a laser assisted CVD process.
Presently, there is a going demand from the industry for microprocessing of materials. In particular, for application in the field of microsystem technology it is necessary to produce structures with dimensions down to the micrometer scale in various materials. We have been investigating the structuring of silicon, anodic bondable PYREX glass, Al2O3-ceramic and PMMA by means of laser microprocessing using an excimer laser and TEA CO2 laser. Both the mask projection technique and the focusing technique have been employed. We will show the dependence of the ablation thresholds and the ablation rates on the laser parameters and on the physical properties of the materials, i.e. absorption coefficient, melting point and thermal conductivity. During and after the laser processing of different glasses we observed the formation of cracks in the laser irradiated region and partly in the glass wafer surrounding the drilled holes. Those crack formations should be due to the developed of thermally induced mechanical stress in the glass.
The laterally resolved absorption and the laser damage thresholds at 1.06 micrometers wavelength of yttria and hafnia films prepared by pulsed laser deposition with oxygen ion bombardment of the growing films were investigated. Depending on the laser and ion beam parameters films with low average absorption can be prepared by that method. Consequently, high predominantly intrinsic absorption induced laser damage thresholds D1 comparable with those of continuously evaporated films can be prepared. The more defect induced laser damage thresholds D0, however, are largely determined by a certain number of micron- sized particulates embedded inside the films. Their number can be reduced by optimizing the laser pulse power density and the laser beam cross-section on the target, while their influence on laser damage thresholds can be reduced by increasing the ratio of oxygen ion bombardment to growth rate.
Hafnia, zirconia and yttria films for optical applications were prepared by laser ablation using an excimer laser at 248 nm wavelength. Films were deposited at room temperature either in an oxygen atmosphere or with additional oxygen ion bombardment of the growing films. We will show that laser ablated oxide films have a high refractive index approaching that of the corresponding bulk material and, hence, a high packing density. Moreover, the films possess high laser damage thresholds at 1.06 micrometers wavelength, though they are still somewhat lower than those of good electron beam evaporated films. Oxygen ion bombardment leads above a certain threshold of ion energy and current density to a decrease in refractive index. In the case of hafnia, for example, it decreases from 2.15 down to 1.80 at 600 nm wavelength. Experimental proof will be given that this behavior is a result of ion induced modifications of microstructure. While films with high refractive index were of amorphous structure and had a high packing density with low porosity, increasing ion bombardment of the growing films leads to increasing crystallization within the films and, finally, to polycrystalline films combined with increasing grainlike film growth. Larger voids between the grains result in lower packing density and, therefore, lower refractive index. Based on these findings multilayer systems of only one material with ion controlled refractive index variations were prepared and investigated with regard to their laterally resolved absorption and their laser damage thresholds.
Excimer laser ablation of a polycrystalline graphite target was used to prepare amorphous carbon films. Optical properties of the films were investigated in dependence of the laser power density and the hydrogen supply during deposition. The hydrogen content of the films was 0.7 to 37.5 at % in dependence of the deposition conditions. An optical bandgap up to 1.6 eV was found for films with low hydrogen content. Applying an additional hydrogen plasma during deposition the optical bandgap increased up to 1.95 eV. The laser power density was varied between 1.5 and 3.4 X 107 W/cm2. Generally, the lower power densities near the ablation threshold lead to larger optical bandgaps. An additional excimer laser irradiation of the growing carbon films with a laser power density up to 106 W/cm2 leads to graphitization within the otherwise amorphous films. An increase of the laser power density to 2 X 106 W/cm2 induce the formation of microcrystallites. Those microcrystallites could be identified as cubic diamond by means of transmission electron microscopy (TEM) investigations.
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