Beyond the Yablonovitch limit: Trapping light by frequency shift

It is shown that randomizing the photon distribution over the frequency as well as orientation variables dramatically improves the efficiency of optical confinement in a weakly absorbing material such as crystalline silicon. The enhancement in average optical path length over the Yablonovitch limit [E. Yablonovitch, J. Opt. Soc. Am. 72, 899 (1982)] is given by an inverse Boltzmann factor of the frequency shift, making it possible to manufacture, for example, efficient crystalline silicon solar cells of thickness barely 1 μm.