APPLICATIONS Study of the high throughput flexographic process for silicon solar cell metallisation Sébastien Thibert 1,2,3 * , Johann Jourdan 1 , Bernard Bechevet 1 , Simon Mialon 1 , Didier Chaussy 2,3 , Nadège Reverdy-Bruas 2,3 and Davide Beneventi 2,3 1 MPO-Energy, Domaine de Lorgerie, 53700 Averton, France 2 LGP2, Université Grenoble Alpes, F-38000 Grenoble, France 3 LGP2, CNRS-Grenoble INP-Pagora-Agefpi, Grenoble, France ABSTRACT A commercially available silver paste was modified to match the flexographic process requirements. Rotational and os- cillatory rheological tests were carried out to assess the printability and spreading behaviour of the resulting inks. Then, a multifactorial approach was used on a laboratory-scale printing press to adapt the flexographic process for the front side metallisation of Cz-Si solar cells, especially for the seed layer deposit of two layer contacts. To quickly identify the significant process parameters, a fractional design of experiment based on a screening approach at two levels was performed. Afterwards, two full factorial designs of experiments were implemented. While the first one allows a better understanding of the effect of the main factors and interactions, the second allows a fine tuning and a confirmation of the first results. Additionally, this methodology allows corroborating the influence of the ink rheological properties on the printing results. Following the process study and optimisation, a seed layer with an average width of 25 μm was printed at a high 0.3 m/s throughput. Additional results suggest that the line width and the throughput can be further improved, which underlines the potential of flexography for photovoltaic applications. Finally, the light-induced process was used to thicken the seed layer after a standard firing-through step, leading to an encouraging 17.9% efficiency on Cz-Si solar cells. Copyright © 2015 John Wiley & Sons, Ltd. KEYWORDS front side metallisation; flexography; light-induced process; rheology; seed and plate contacts; silicon solar cells *Correspondence S. Thibert, LGP2 Grenoble INP-Pagora, 461 rue de la Papeterie CS 10065, 38402 Saint-Martin-d’Hères, France. E-mail: Sebastien.Thibert@lgp2.grenoble-inp.fr Received 10 November 2013; Revised 24 January 2015; Accepted 22 June 2015 1. INTRODUCTION Although screen printing is still seen as the dominant metallisation process for the forthcoming years [1,2], it strongly affects the cost and the performances of commer- cial silicon solar cells. Among the alternative solutions, the ‘seed and plate’ [3] metallisation is cost-effective [4] to re- produce the finger structure of high efficiency solar cells [5] without the need of expensive photolithography steps. The seed layer allows optimising the mechanical and elec- trical properties of the contact, while the conductive layer provides the high finger conductivity needed to limit the grid power losses. Most of the time, the second deposit is grown on the seed layer using the light induced process [6] with silver or copper (Ag-LIP or Cu-LIP). As the first layer should be as narrow as possible to reduce optical losses and material consumption, several solutions [6–10] have been developed to overcome the limited screen print- ing resolution. Some, such as inkjet and aerosol printing processes, are based on the classical firing of a silver and glass frit mixture to contact the emitter through the antire- flection coating [6–8]; others are based on a more innova- tive laser opening process followed by the deposit of a self- aligned nickel seed layer [9,10]. Although these processes have demonstrated very good results at a laboratory scale, it is still challenging to implement them in mass production because of throughput and cost issues. In contrast, in other industries, the inexpensive flexographic printing process has already proven its ability to deposit a low ink volume on uneven and fragile substrates at a very high throughput PROGRESS IN PHOTOVOLTAICS: RESEARCH AND APPLICATIONS Prog. Photovolt: Res. Appl. (2015) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/pip.2659 Copyright © 2015 John Wiley & Sons, Ltd.