How big is the spot? If it's a tiny little dot, then most likely a dead or stuck pixel and had nothing to do with being charged on a solar charger, it was just coincidence. There is not much your can do to fix it other than replace the screen.
The information on Computing.Net is the opinions of its users. Such
opinions may not be accurate and they are to be used at your own risk.
Computing.Net cannot verify the validity of the statements made on this
site. Computing.Net and Purch hereby disclaim all responsibility
and liability for the content of Computing.Net and its accuracy.