I'm studying material science at the university of Wisconsin, so please trust my words over these pseudoscientific quacks.
There are many compounds that can be made into solar panels. I won't get into why but they are usually semiconductors and besides the type of semiconductor the processing of the cell makes a difference.
They are toxic. Quite toxic. But not nuclear waste toxic. I think the metals within them are well contained, and in small quantities. They are also solids with high melting points and not a great propensity to dissolve if certain thermodynamic factors are considered.
All in all this is a stupid idea though. The biggest problem with solar panels is their cost, because they ultimately don't cost that much less than natural gas. This difference is created by efficiency and durability. These solar panels will go into disrepair very quickly, and the tracking of mud into the highway will reduce their efficiency by a lot during rainier seasons. Good luck creating a glass that can endure that kind of abuse.
Piezoelectric materials are also the future.
Go badgers.