Laser scribing and printing processes for thin-film PV devices

Abstract

Generic processes such as depth-selective laser scribing and the printing of insulating and conductive tracks that can be cured at low temperature, are a key requirement to enable cost efficient production of advanced thin-film PV concepts. In contrast to TCO glass based superstrate device concepts, no standard laser scribing processes and manufacturing tools to achieve fully monolithic series interconnection are presently available for so-called substrate type device concepts that are built on — often opaque and/orflexible — substrates. Three key features of such advanced interconnection processes are presented here: laser scribing, printing and electrical modeling. As vehicle to develop and demonstrate these interconnection processes, a novel roll-to-roll concept for fabrication of thin-film silicon solar cells on steel foil is chosen. We show that laser scribing of amorphous silicon solar cells with a 1064 nm ps laser leads to a minor loss in efficiency. The screen printing process of low-temperature curing Ag paste is also proven not to degrade the device performance, and by modeling the module interconnection, we calculated losses below 10% when going from individual cells to modules. Efforts are underway to realize large area solar cells with printed current collecting grids, and finally a fully series interconnected module by combining laser scribing and printing as cost-effective processing operation.