Physically, the panel efficiency in part depends on the type of solar panel uses. Most of the Solar Chargers for mobile phones on the market are the first-generation crystalline silicon. Does it matter if the solar power bank gets very hot from sitting in the sun? especially if the temperature is above 40+ C?
BTW the photos are good and has a much detail explanation. You can make some tear down video. @proteus-h
Temperature increases will likely cause problems, but this can be avoided by circulating air around the battery, like if you clipped it you a backpack and walked around with it all day. Hence why I think this battery is ideal for hiking.