Russell Ohl (Wikipedia) is generally credited with inventing the first “modern” solar cell. His 1946 patent for a “Light sensitive electrical device” inspired an unnamed British science teacher from Surrey to create a working version of the device, which was recently discovered by his family and found to still work perfectly. In full sunlight, it generates 1.5 volts. According to this article in The Daily Mail:
[I]t was not until Russell Ohm [sic] patented the idea of the junction semiconductor solar cell, that the modern day solar panel was born. It is not known whether the American actually built a version of his modern solar cell, which means this artefact is thought to be the first one.