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)Se2 (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.

Transparent back‐junction control in Cu(In,Ga)Se2 absorber for high‐efficiency, color‐neutral, and semitransparent solar module

“…It thus enables see‐through scribing with a clear‐cut edge morphology at a much lower laser power density and without requiring removal of the ITO layer. The lower energy threshold for P4 scribing is beneficial because CIGS easily melts when heated by a focused laser, 19–21 and the molten CIGS debris after P4 scribing can function as a shunt path in the device 17 …”

“…Recently, we demonstrated the feasibility of making apertures in CIGS thin films using a controlled see-though laser-scribing process. 17 Such aperture-type TPVs would enable the manipulation of the PCE and transparency through adjustment of the aperture ratio, [4][5][6][7][8] and a high-efficiency TPV with better color neutrality compared with TPVs fabricating using competing technologies might be possible. To make aperture-type TPVs esthetically appealing to consumers, the formation of an invisible see-through pattern is critical.…”

“…The lower energy threshold for P4 scribing is beneficial because CIGS easily melts when heated by a focused laser, [19][20][21] and the molten CIGS debris after P4 scribing can function as a shunt path in the device. 17 Although the use of an ITO back contact offers a broad P4 scribing window, using an oxide back contact is not trivial because of parasitic GaO x formation at the ITO/CIGS interface as a result of the reaction between the Ga in CIGS and the O in ITO during CIGS deposition at 550 C. [22][23][24][25][26] GaO x is a wide-bandgap semiconductor and is prone to n-type conduction 27 ; it therefore hinders hole transport at the back junction. Figure 3A shows the current density-voltage (J-V) characteristics of CIGS solar cells with an ITO back contact.…”

“…A further expanded view more clearly reveals molten CIGS debris at the edge; however, the location of the debris does not appear to cause a shunt path between the ITO and the top AZO electrode. At a higher laser power, however, molten CIGS debris is left along the sidewall, as shown in Figure7D, which can function as shunt paths between the ITO bottom and AZO top electrodes because of the Cu-rich character of the molten phase 17.…”

Real-Time Monitoring and Defect Detection of Laser Scribing Process of CIGS Solar Panels Utilizing Photodiodes

“…Hence, it leads to decreased efficiency resulting from the loss of the active solar cell area [5], [6]. Laser scribing technology has been actively developed in recent years and is replacing conventional mechanical methods for CIGS cell scribing [4], [7], [8]. In addition to advantages such as manufacturing accuracy, controllability, and high power of laser beam, laser scribing provides more other benefits than mechanical scribing to produce CIGS cells.…”