@warren taking notes here on techniques for DIY solar cells. Some are more toxic than others.
Titanium and berry based
(Variation of https://en.wikipedia.org/wiki/Graetzel_cells)
- https://www.instructables.com/id/homemade-solar-cell-using-household-items/
- https://www.instructables.com/id/DIY-solar-cell-from-scratch/
- https://www.wikihow.com/Make-Solar-Cells
- https://www.instructables.com/id/How-to-Build-Use-A-Dye-Sensitized-Solar-Cell-DS/
- https://edu.rsc.org/resources/make-a-grtaand776zel-cell/1290.article
Copper-oxide-based
- http://cleanenergywiki.org/index.php?title=Cuprous_Oxide_Solar_Cell
- https://www.newphysicist.com/diy-solar-cell-cuprous-oxide/