Solar cells could get an efficiency boost of 30% using a device proposed by physicists in Australia and Germany. Martin Green of the Centre for Third Generation Photovoltaics at the University of New South Wales and colleagues say that ‘down-converters’ could be connected to existing solar cells to double the number of ‘useful’ photons they capture (T Trupke et al 2002 J. Appl. Phys. 92 1668).