"What's that black strip on top of the solar panel?" The second photo is a close-up of the junction box on one of my portable solar chargers. This box's job is to connect the wires inside the solar panel to the two wires on the outside.
It sounds simple, but these little boxes have to undergo a huge range of testing and engineering before ending up on the panel. They need to be waterproof and durable. The wires inside the solar panel are flat like noodles, connecting each of the dark blue solar cells together without adding to the panel's thickness.
In the junction box, these flat metal strips meet photovoltaic wire, which has a thick UV resistant jacket to protect from constant sun exposure. These outer wires are then paired with MC4 connectors, a locking connector for solar. Our tripod chargers are waterproof all the way up to your battery thanks to this little box!