Mars rover, self cleaning solar cells!

Not by design but it is now thought electrically charged dust devils attracts dust gathered on solar cells, extending the lifetime of Opportunity WAY past it's design life which was only 3 months.
It sounds like future robots could be equipped with charge devices that do that job any time it needs it.

https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html

Now a reality, at least in the labs:

YouTube

BTW, tandem solar cells, perovskites with IR now up to 24% efficiency:

https://phys.org/news/2018-09-perovskitecigs-tandem-cell-efficiency-percent.html#nRlv