[gradschoolfail]

Maybe indium in ITO for those fancy transparent front contacts. Or tellurium in CdTe, supposedly still costeffective compared to “thick” Si cells. I would still give GGP a break it can be tricky to venture even small steps outside ones specialty these days

[pfdietz]

And, maybe in the future, gallium as a dopant in silicon cells, since it doesn't experience nearly as much light induced degradation as boron does. But dopants are used in very small amounts.

I think some power electronics uses europium silicide (or was that erbium?) as a gate material, so maybe in inverters? Again, the quantities would be small.