the solar panels in screen size nearly cannot charge the battery, and it heat up the phone probably cause damage of the battery. an external solar pack is more

the solar panels in screen size nearly cannot charge the battery, and it heat up the phone probably cause damage of the battery. an external solar pack is more practical. btw, thanks your question hints me another solution, if solar pack can be more slim and foldable, it will be great to be a "solar-phone-case".