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combinations until an optimum cleaning result was achieved.
To evaluate how deburring affects photovoltaic efficiency, organic photovoltaic modules eight centimeters wide were produced on substrates that had been
cleaned using the CO2 snow-jet process. These were compared with modules produced on untreated substrates and manually-cleaned substrates of the same size. As expected, the modules on the uncleaned substrate had a high leakage current, which reduced Photovoltaic Cell Efficiency (PCE) to 2.3%. For the manually cleaned modules, the PCE was 4.8%, and
Fig 3 The effects of deburring were demonstrated by measuring the IV curve of modules produced
on substrates that were untreated (d), manually cleaned (e) and cleaned using the CO2 snow jet technology (f). b and c show the light and dark curves of the three differently-treated modules. In the DLIT images of the modules (d, e, f), the bright areas indicate hot, localised spots, which are particularly visible in the interconnection zones of the uncleaned modules.
snow crystals. These are bundled by a separate jacket jet of compressed air and accelerated to supersonic speed. When the easily-focused jet of snow and compressed air impacts on the surface to be cleaned, a combination of thermal, mechanical, solvent and sublimation effects occur, which is the basis of the cleaning action. The crystalline carbon dioxide sublimates completely during the process, leaving the treated surfaces completely dry.
Proven efficient burr removal and enhanced efficiency
A roll-to-roll pilot line was set up for cleaning the laser-structured electrode substrates and fitted with several quattroClean snow jet nozzles arranged above the electrode web. The first step was to optimise the jet parameters so as to significantly reduce the burr height without damaging the electrode.
for the modules cleaned using the CO2 snow-jet process, it was as high as 5.3%. The difference in efficiency is explained by the fact that manual cleaning causes scratches to be formed on the electrode, which can significantly reduce the active area. This
Fig 4 The thickness of the layer stack (without the PET layer, which serves as a carrier material for the layer stack) of a printed solar cell (ETL electron transport layer, AL active layer, HTL hole transport layer, AgNW silver nanowire electrode, IMI electrode is laser structured) is well below one micrometer.
In addition to the capillary diameter, which determines the flow rate of the liquid carbon dioxide, and the pressure of the compressed air jacket, the distance between the nozzle and the substrate needed to be adjusted, as well as the web speed and the inclination of the nozzles in relation to the substrate. After each cleaning process, the maximum burr height was measured by confocal microscopy. This procedure was repeated for a large number of parameter
is because the scratched area does not generate any current and also because areas can be cut off from the charge extraction by the scratch.
Dark Lock-In Thermography (DLIT) was used to confirm that deburring is responsible for the difference in efficiency of the differently- treated substrates.
Ready for series production for various applications
The fully automated cleaning solution has now been integrated into the standard production process for printed photovoltaics at the Institute Materials for Electronics and Energy Technology. Here, an array with seven nozzles is used to reliably remove the laser-induced burrs on a 25 cm-wide web.
At Sciprios, too, the CO2 cleaning process is now one of the equipment options for roll-to-roll production lines for printed photovoltaic modules.
The 300R2RCompact R&D platform, into which the cleaning solution can be easily integrated, enables a wide range of roll-to-roll coating and printing experiments to be carried out. It can also be used to upscale laboratory tests to small production series.
The cleaning solution, which is easily integrated into roll-to-roll production lines, makes the manufacture of any type of printed electronics involving laser structuring more economical, more productive and more sustainable. Another application is electrode production in battery manufacturing.
APRIL 2024 | ELECTRONICS FOR ENGINEERS
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Photo credit: Sciprios GmbH
Photo credit: Research project team PV-CO2
Photo credit: Research project team PV-CO2
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