Polycrystalline CdTe on CuInSe/sub 2/ cascaded solar cells

Experimental results obtained using a CdS/CdTe/ZnTe top cell on a CdS/CuInSe/sub 2/ bottom cell are presented. Single cells of each type exhibit an 11% efficiency. The fabrication of a mechanically stacked CdTe-CuInSe/sub 2/ tandem cell that shows an efficiency of 9.9% is discussed. The current of the CuInSe/sub 2/ cell is limited by the transmission through the CdTe cell. Semiquantitative analysis of the optical losses in the structure indicates that substantial improvements in tandem device performance can be achieved by: reducing free carrier absorption in the transparent (SnO/sub x/) top contact, e.g. by using an alternative transparent contact such as ITO or ZnO which has better near-IR transmission, and reducing the absorption in the Cu-doped ZnTe layer-perhaps by reducing the Cu doping level.<
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