Printing technologies for current collectors for dye-sensitized solar cells.

Abstract

This project was in collaboration with TATA Steel Colors to investigate printing technologies for current collection grids in dye-sensitized solar cells (DSCs) for high volume, large area production. Current collecting grids are important to reduce resistive losses and maintain performance. The aims of the thesis were to; investigate different high volume printing technologies as an alternative to screen printing for depositing current collector grids, develop a fast drying and sintering method for improved manufacturing speed, and to develop monitoring technology for quality control to optimize production. Flexographic printing was identified as an alternative to screen printing. Flexible DSCs produced with a flexographic printed current collecting grid were found to have an efficiency drop of -33%, when compared cells built with screen printed current collecting grids. However, the amount of silver printed using flexography saw a reduction of -95% offering a significant reduction in materials cost. A barrier to high volume roll-to-roll printing of conducting inks is the time required for drying and for nanoparticle inks sintering. Nanoparticle inks require a secondary sintering phase to form a highly conductive metallic film. Near infrared (NIR) radiation has been shown to be a rapid method for drying and sintering a silver nanoparticle ink in just 1 second, compared to 10 minutes in an oven, offering a significant reduction in process time. Polymer thick-film inks with microparticles require thermal treatment to remove the solvent to facilitate particle contact which allows the ink to become conductive and NIR drying was found not to be effective. Quality control of the sintering process of silver nanoparticle inks is carried out offline. A method which could be implemented inline has been developed using colorimetry to correlate the colour of a silver nanoparticle ink film to its electrical performance using CIELAB colour coordinates. It is a fast, non-contact method. The technique works on the principle of light scattering through nanoparticles

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