Nanosecond laser scribing for see-through CIGS thin film solar cells

Abstract

Building-integrated photovoltaic (BIPV), especially in a semitransparent and/or see-through configuration, has attracted significant attention because of the extended surfaces available for the photovoltaic (PV) installation including roofs, facades, and windows. In this study, we examine the P4 scribing process for fabricating see-through cells on a new Cu (In,Ga)Se-2 (CIGS) architecture with indium tin oxide (ITO) bottom contact, using a nanosecond laser beam of 532-nm wavelength illuminated from glass substrate side. Through parametric studies with the variations of laser beam spot size and pulse energy, we have identified that enlarged laser beam with the pulse energy near scribing threshold could suppress both damage in ITO and electrical shunt induced by molten CIGS. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses unveil that the molten CIGS mediated shunt mechanism, wetting the scribing edge and forming Cu-rich metallic phase. The P4 scribing process operated near threshold fluence of enlarged laser beam clearly suppressed unwanted shunt, also minimizing the fluctuation in the desired film removal trend. Thermal analysis supports that enlarged laser beam enables scribing at reduced CIGS-ITO interface temperature assisted by buckling-based film delamination mechanism and also suppresses CIGS melting at scribing edge and its neighborhood. See-through cells fabricated for the areal fraction of approximately 15% using the optimal laser scribing parameters exhibited the short circuit current reduction rate of 16.8% enabled by the low shunt resistance reduction rate of approximately 8%. Further studies are underway to elucidate precise shunt-related scribing mechanism on the basis of the cross-sectional analyses and time-resolved diagnostics and to fabricate the module level see-through PV architectures.