A tandem photovoltaic device includes at least two photovoltaic cells stacked in an optical and electrical series relationship. At least one of the tandem cells includes a dual function semiconductor layer fabricated from a dual function semiconductor material. This dual function layer is an electronically active constituent of the cell. The dual function layer also is optically active and creates a reflective condition which redirects a portion of the light which has passed through the cell back through the cell's active layers to photo generate additional photocurrent. Use of the dual function material eliminates the need for incorporating separate semiconductor and reflective layers in a photovoltaic device. Further disclosed are exemplary formulations of some dual function materials.
STATEMENT OF GOVERNMENT INTEREST
 This invention was made with government support under contract DE-FC36-07GO17053 awarded by the Department of Energy. The United States Government has certain rights in the invention.