Current Collecting Grids for R2R Processed Organic Solar Cells
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Current Collecting Grids for R2R Processed Organic Solar Cells Robert Abbel1, Jaquelien van den Boomen1, Tim van Lammeren1, Tom de Koning2, Josué J. P. Valeton3 and Erwin R. Meinders1 1 Holst Centre – TNO, High Tech Campus 31, P.O. Box 8550, 5605 KN Eindhoven, The Netherlands. 2 Fontys University of Applied Sciences, P.O. Box 347, 5600 AH Eindhoven, The Netherlands. 3 NeoDec BV, Raiffeisenstraat 9, 5611 CH Eindhoven, The Netherlands.
ABSTRACT Exposure to highly focussed flash light (photonic flash sintering) has been developed as a technology to successfully cure printed metal inks on temperature sensitive plastic substrates. In contrast to the traditional approach of thermal oven sintering, conductivities up to 30 % of the value of bulk silver can be achieved within a few seconds without foil deformation. The compatibility of this technology with R2R production has been demonstrated with line speeds up to 5 m/min. As a consequence, our approach is expected to enable the high throughput fabrication of current collecting grids for organic solar cells in order to replace transparent electrodes based on metal oxides such as ITO. Additionally, our new sintering technology has enabled us to process a new generation of conductive inks, based on copper complexes, which cannot be processed by oven sintering. INTRODUCTION An important component in organic solar cells is a transparent electrode through which the incident light can reach the active layers [1]. The materials currently available, such as transparent conductive oxides (TCOs) [2] or conductive polymers [3], however, generally suffer from relatively low conductivities, resulting in resistive losses [4]. A consequence is a decrease in energy conversion efficiency, which is especially severe in large area devices [5]. In addition, inorganic TCOs tend to be rather brittle, which causes difficulties when they are applied on flexible substrates. A solution to these problems is the use of a combination of a transparent polymer layer with moderate conductivity and a highly conductive metal grid in the OPV architecture [6]. A way to deposit the latter structures is the printing of metallic inks [7], which currently are almost exclusively based on silver. After printing, high conductivities are usually achieved by oven sintering at elevated temperatures, which, however, is incompatible with most plastic foils and high throughput R2R manufacturing [8]. Various faster alternatives have therefore been examined, including photonic flash, microwave, laser, electrical, plasma and chemical sintering [9,10]. At Holst Centre, we are investigating the potentials of such fast sintering technologies for their application in the R2R production of printed electronic devices, among which polymer solar cells. Our most mature method at the moment is the exposure of printed metal structures to short and highly focussed flashes of visible light (photonic flash sintering). In the following, we will present some results obtained with silver and copper based conductive inks on plastic foils and
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