Is perovskite solar cell efficiency more hype than reality?

Reports now suggest they are capable of efficiencies greater than 20% – a milestone which took other solar cells decades to reach.
But how realistic are these efficiency values? This question is now being asked by national laboratories, with a cluster of research groups finding that the very nature of efficiency testing, as well as the questionable stability of perovskites themselves, is only serving to exaggerate device performance. And unless this stability problem can be solved perovskite devices may never become a viable alternative to silicon solar cells. 

He talks to Keith Emery, chief scientist at the National Renewable Energy Laboratory’s (NREL) photovoltaic cell and module performance characterisation group in the US, who says, 

All the exciting efficiencies and any energy claims that are associated with [perovskite solar cells] should be taken with a grain of salt…
To solve the stability problem the economics of that material system may go out the door. Until the stability problem is solved, you do not know how much it is going to cost you.’

Martin Green, director of the Centre for Advanced Photovoltaics in Australia, agrees:

Measurement is complicated by the fact that devices are not stable,’ says Green. ‘They display hysteresis in their output.

Cosmos magazine looked at the progress of research into alternatives to silicon in solar cell manufacture last week.