Biodegradable electronics?
There's something good about this, but at the same time, having to replace all your solar cells in 9 months (or even after an unusually hot day - proteins are much more temperature-sensitive than silicon) doesn't quite sit well with me.
Maybe in portable, handheld devices (insert argument about planned obolesence, etc..)
Some proteins last for a very long time, hair for instance is found on mummies 5000 years old, leather is another one that comes to mind some fungus spores can exist for hundreds of years and still grow at the end of that time so can many bacteria and viruses, so as long as the protein used in the solar cells is stable and prevented from oxidizing there should be no reason not to expect a long life from them.