OPV cells are expected to be much lower efficiency than traditional photovoltaics, but make up for it by being even lower in cost by comparison.<p>To me it's never seemed like "inexpensive" and "indium" belong in the same sentence.<p>So off the top of my head I would say graphene which is just fancy carbon rather than a rare element like indium.<p>I would want to try them both in the lab but if you scale up there's probably not enough indium to go around no matter how thin you spread it.