Development of Cu plating for silicon heterojunction solar cells

This paper reports the results of the study comparing various patterning and plating methods for the deposition of Cu electrodes on transparent conductive oxides for silicon heterojunction solar cells. We compared direct electroplating of Cu on different metal seeds (Ag, Ni, Cr and Ti deposited on transparent conductive oxide by physical vapor deposition) to the light induced plating of Ni/Cu directly on transparent conductive oxide. Patterning was done either using photoresists (formed by spin-on, screen printing or lamination) or lift-off of the PECVD dielectric using screen printed resist. The geometry of the fingers, line resistance, contact resistance and adhesion were used as comparative parameters. We identified direct electroplating of Cu on the sputtered Ag seed to achieve the lowest contact resistance and the best adhesion. All photoresists were able to achieve less than 60 micron resolution and could produce the fingers with the sought height (some, however, having a characteristic mushroom shape). The best silicon heterojunction cell with Cu contacts directly electroplated on the sputtered Ag seed achieved 21.9% efficiency on 153 cm² area.