A down-converting (DC) layer placed on the front side of a silicon solar cell has the potential to generate more than one low-energy photon for every incident high-energy photon. Recent theory has predicted that DC in conjunction with a silicon solar cell can achieve a conversion efficiency of up to 38.6%. This paper examines the application of rare-earth-doped inorganic materials for achieving external quantum efficiencies greater than unity and enhancing the conversion efficiency of silicon solar cells. Such DC mechanisms have been applied in similar phosphor materials used by the lighting and display industries. The opportunities for the DC of high-energy solar photons to multiple photons with energy greater than the silicon bandgap are discussed. (c) 2005 Elsevier B.V. All rights reserved.