Development of high-efficiency Al/sub 0.2/Ga/sub 0.8/As solar cells and interconnect schemes for Al/sub 0.2/Ga/sub 0.8/As/Si mechanically-stacked cascade cells

Al/sub 0.2/Ga/sub 0.8/As/Si mechanically-stacked cascade cells offer potential AMO power conversion efficiencies >25 percent. The demonstration of a high-performance stack requires three critical components, a high efficiency (/spl sime/18 percent) Al/sub 0.2/Ga/sub 0.8/As top cell, a high-conductance interconnect, and a high-efficiency Si bottom cell. In this work, the authors present the development of a 17 percent (active-area) efficient p/sup +/-n Al/sub 0.2/Ga/sub 0.8/As solar cell. The cell has a V/sub oc/ of 1.22 V, a J/sub sc/ of 21.8 mA/cm/sup 2/, and a fill factor of 0.865. The Al/sub 0.2/Ga/sub 0.8/As cells were grown by low-pressure organometallic vapor phase epitaxy. The introduction of an undoped spacer layer between the n-base and the p/sup +/-emitter is found to improve the fill factor and the red response of the cells. Second, they report an interconnect scheme for the mechanical stacking of the AlGaAs cells onto a Si substrate. The technique involves an eutectic-metal-bond (EMB) using a Au/Sn/Au metallization between GaAs (contact layer to the base of the AlGaAs cell) and Si. Preliminary evaluation of this EMB interconnect reveals a resistivity of /spl sime/4.2/spl times/10/sup -2/ ohm-cm/sup 2/ which is adequate for AMO operation. The advantages of this interconnect for the p/sup +/-n cell configuration, including suitability in manufacturing environment for the production of low-cost AlGaAs/Si mechanically-stacked cells, are presented.<
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