Solar Cells - What's the Key Development?

University of New South Wales was in competition with groups at Stanford University and Levan University for pushing the efficiency of solar cells up and up. And we, all three groups contributed very substantially. A 20% conversion efficiency means that 20% of the energy in the incoming sunlight ends up as electricity and the other 80% gets lost as heat. It's obviously desirable to have a high efficiency because then you need less land and transport and fencing and support structures. But you can't afford to pay too much for that high efficiency. Otherwise, you'll have a wonderfully efficient solar cell, which is prohibitively expensive and only use all in space, for example.