A photovoltaic device having a down-converting layer disposed on the device, is presented. The down-converting layer have a graded refractive index, wherein a value of refractive index at a first surface of the down-converting layer varies from a value of refractive index at a second surface of the layer. A photovoltaic module having a plurality of such photovoltaic devices is also presented.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT
 This invention was made with Government support under contract number DE-EE0000568 awarded by Department of Energy. The Government has certain rights in the invention.