The most efficient thin-film solar cells include toxic or rare materials, such as cadmium, ruthenium and lead, as well as hazardous organic solvents.

Unfortunately, many of the successes so far have come through the use of scarce and expensive metals such as palladium, platinum, ruthenium and iridium.

Certain minerals such as gold, platinum, silver, tungsten, iridium, osmium, palladium, rhenium, rhodium and ruthenium might be mined and transported to Earth for on-planet use.