There's a difference between test bed efficiency and real world due to weather. The reason solar cells for space are so efficient is the solar spectrum doesn't change and the multi-junction cells are optimized for the AM0 spectrum. Put the same cells down here on earth and they are only reach peak efficiency around solar noon on blue sky days.
Instead of improving the electricity yield of existing technology, a research team has been able to convert light into electricity that has not yet been used. Efficiency is expected to increase by two thirds - and all without rare-earth elements.