Femtosecond events dictate efficiency of future solar cells

The research, at the Universities of Cambridge and Milan, studied how quickly electrons created as sunlight hits the solar cell material need to reach the cell’s electrode to be converted into flowing electric current before their energy starts to decline. The teams, led by Prof Sir Richard Friend at St John’s College, Cambridge, and Prof Guilio Cerullo at the Polytechnic University of Milan, found that this time is of the order of 10 femtoseconds — a femtosecond is 10^-15 seconds, or a millionth of a billionth of a second.

If the cells can work that fast, they could achieve an efficiency of 30 per cent or possibly greater — in rough terms, the greatest efficiency that solar cells could conceivably achieve. Today’s best silicon-based solar cells typically operate at efficiencies closer to 20 per cent. But perovskite cells are much thinner than silicon cells, which gives the team hope that this speed could be achieved.