Patterning and Metallization of Silicon Solar Cells by Inkjet-Printed Functional Ink on a Photoresist Layer Zhongtian Li, Ran Chen, Yu Yao, Wei Zhang, Xi Wang, Ivan Perez-Wurfl, and Alison Lennon The University of New South Wales, Sydney, NSW, 2052, Australia Abstract — This paper reports a patterning and metallization method for silicon solar cells fabrications. Patterning was achieved by the inkjet printing of a dye-based ink as a mask to protect the photoresist from UV-light initiated crosslinking. The patterned photoresist was used to facilitate the etching of a pattern in the underlying dielectric layer and also to act as a metal plating mask. This method resulted in fine point openings in the photoresist layer with a diameter of 15 μm and line openings with a width of 30 μm. Nickel/copper plated homogeneous emitter silicon solar cells with an efficiency of 18.2% on small size Cz wafers were fabricated using this method, may find applications in the metallization of future heterojunction, rear contact and PERC cells. Index Terms — patterning, metallization, photolithography, inkjet, photovoltaic cells, silicon. I. INTRODUCTION Photolithography has been used to fabricate high efficiency solar cells such as the PERL cells at UNSW and the A300 cells at Stanford University. It requires a rigid photomask which is generally made using a transparent quartz chip and a patterned chromium or chromium oxide shielding layer [1]. The fabrication of photomasks requires expensive facilities and advanced technologies. Furthermore, chromium is environmentally hazardous which contributes to photolithography not being a cost-effective patterning technique for commercial solar cell production. Inkjet printing has been used for patterning in both industrial and scientific applications (see [2] for a review). Unlike the nanoscale patterning requirements for semiconductor integrated circuits, patterning with a resolution of several micrometers is generally sufficient for solar cells. With inkjet printing, printed features less than 20 μm in width are achievable [3, 4]. The use of inkjet printing to construct conformal masks for patterning photo sensitive films has been reported [5]. Patterns of an ink, capable of absorbing UV light, were printed on substrates coated with photoresist using a piezoelectric inkjet printer. After UV induced polymerization and ink removal, the designed microstructure pattern was realized with feature sizes (e.g., microchannels) as small as 60 μm. However the dried ink thickness had to be more than 1.8 μm to successfully block the UV light. In this paper an inkjet facilitated maskless lithography method in fabricating solar cells was reported. After forming the patterned mask, different processes can be applied for various applications. For example, if the underlying layer is a transparent conducting oxide, then copper can be plated directly onto the oxide through the openings in the mask. Alternatively, after etching a dielectric through the patterned openings, rear point or line openings in the dielectric can be used for rear contact or PERC cell structures. In the work reported in this paper, the patterned photoresist was used as: (i) an etching mask to make line openings in a SiNx layer; and (ii) a plating mask for the formation of front metal contacts. II. EXPERIMENTAL A negative photoresist was used in this experiment. After spin-coating at 2000 rpm for 30 s, the photoresist thickness was 4 μm. For alkaline-textured Czochralski (Cz) p-type silicon wafers, the pyramids can be almost fully covered by the resist, however in some cases the wafer surface cannot be completely planarised due to the presence of saw lines on the wafer. A commercial dye-based ink (ink A), used for a desktop inkjet printer, was printed using an inkjet printer (Dimatix DMP 2800) and 1 pL cartridge. Homogeneous emitter cells, of area 4.62 cm 2 with an emitter sheet resistance of 80 Ω/ and a full-area aluminum screen-printed rear electrode were fabricated. A photoresist layer was spin-coated on the alkaline-textured, SiNx-coated emitter, was patterned as shown in Fig. 1. Fig. 1. Fabrication process for patterning the photoresist using the dye-based ink.