This invention improves the efficiency of non-optimal solar cell materials, enabling them to achieve the same efficiency as optimal materials. The invention describes a method of improving the emission and absorption properties of a generic photovoltaic cell using feedback reflectors and/or filters, increasing the open circuit voltage of the cell, and thus the overall efficiency. Specific examples of single junction photovoltaics are detailed, but not limited to. Particularly, semiconducting solar cells in either single- or multi-junction formats are described. The invention can be applied to any functioning solar cell to increase the efficiency, while describing the maximal efficiency available using thermodynamic identities. Other examples are included, such as organic photovoltaic, nanostractured photovoltaic devices, and non-planar geometries. The invention thus enables using non-optimal photovoltaic materials to achieve similar efficiency results as optimal ones, regardless of the designed structure or material used.
STATEMENT OF GOVERNMENTAL SUPPORT
 The invention described and claimed herein was made in part utilizing funds supplied by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 between the U.S. Department of Energy and the Regents of the University of California for the management and operation of the Lawrence Berkeley National Laboratory. The government has certain rights in this invention.