That's an amorphous solar panel. Techniques used are a bit different than a silicon wafer panel. My experience is with buss leads in a wafer which went well with a soldering gun.
Here's some excerpts from a patent on a methodology used to solder the buss wires...
[0005]
Without the adhesive metal layer, the adhesion of the silver layer to the AZO layer is, technically speaking, sufficient to provide good device performance with the highest current and best conversion efficiency. The biggest problem occurs during the soldering process employed to connect a buss wire to the back contact. During this soldering, the back contact is subjected to high temperature (greater than about 220° C.) and solder flux material, a potentially corrosive chemical, which causes delamination between the AZO and silver interface.
[0006]
Delamination is not solely due to poor adhesion (interface strength) between AZO and the silver layers, but due to other factors as well. The factors that affect the delamination include, in no particular order: (1) interface strength (adhesion between the AZO layer and the silver layer; (2) high temperatures applied to the back contact during soldering causing film cracks along grain boundaries; (3) the corrosive flux used during soldering; (4) a combination of high temperature during soldering and the corrosive flux reacting with the silver and causing delamination at the AZO interface; and (5) film stress mismatch between films in the back contact stack causes sever delamination and flux penetration (and corrosion) during soldering due to thermal stress, resulting in delamination at the AZO—silver interface.
If you'd like to read the entire document
https://patents.google.com/patent/US20120088327A1/en