Converting light into heat is by far not as difficult as turning it into electricity. So don't mix this up with the 20-24% efficiency that are achievable in photovoltaics.
http://www.livescience.com/49133-super-efficient-solar-energ...
I was unaware about the steady progress. Still far away from the 90+% thermal efficiency that is possible with solar heating.
My hopes on photovoltaics are on the relatively new contender Perovskite. Really nice to see the steep progress in efficiency there.
http://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit