THE CONFINEMENT OF LIGHT IN SOLAR-CELLS

The upper limit of the absorption increase due to light confinement is presented here on the basis of non-imaging optics, as well as the conditions to achieve it. It is found that the usual Lambertian only gives maximum absorption for weakly absorbed photons but how to make a device fulfilling the conditions of maximum confinement is not known so far. A reduction of the etendue of the escaping light is a way to increase the confinement. Several ways of achieving it are analyzed including the use of microconcentrating covers, of interference gratings and of large entry aperture light confining external cavities.